In my opinion, unless you have had a bottle of juice from a vendor which was fine and then reordered the same flavor from the same vender that then had this chem/soapy taste is probably not due to something they have done, unless that bottle went bad - or they changed the recipe or switched suppliers for their ingredients (they could have also had a bad batch of nicotine but one would assume enough complaints that they would pull from the shelf), its probably your own taste buds and smell receptors. This would be especially true if you detect this everywhere but to a different degree with different brands - because there are differences in how the ingredients are compounded and what with to produce them before they are made into e-liquid. I would still contact the place you bought it especially if they make their own as opposed to relabeling a generic or selling a brand name not their own. Even if you can put it on one vendor, brand etc in your experience you might get closer to the answer especially talking to the chef/chemist making the juice.
before going nutz and buying out 15 online dealers looking for e-juice without this chemical taste The simplest might be to pick a couple of sites or one site that carries different products and get a few sample packs. The three main categories would be to find a vendor that makes their own juice as its ordered (not necessarily customized flavors but hands on in the shop), the vendor that makes/sells under their label but its made commercially, and a brand name juice that you can get many places but is not special to that vendor. Look for sites that offer sample packs where you can pick the flavors you want in it and try variety and maybe mix up the nicotine mgs too.(If you bother to read further you will see the explanation of nic strength and 'taste'). You might not solve your problem but you could very well find a juice out of these that don't have something in them that you taste as a chemical taste (why below)
One problem I have is that very few bottles of e-liquid come with ingredient labels and those that do rarely list everything in the bottle, usually just the nicotine and PG/VG levels, not what flavors/types are used, sweeteners and preservatives. At least in the US they apparently do not have to be labeled.. I know the bottle is small for an ingredient label, but if there was a law that they had to say everything that is in the e-juice you would get an insert with the juice listing them if they did not fit. This has always bothered me a bit as recipes vary from place to place. For the most part, because of DYI people just assume its nicotine, PG/VG, flavor and that's it when, if full ingredients would be listed you would not only be seeing nicotine and PG/VG in the list but natural as well as (in most cases) artificial flavor, sweeteners (if applicable), preservatives and so on. If labeling feel under the FDA drug laws you would even see what made up artificial flavors or given the correct chemical name to look them up yourself. Most vendors do even post a full ingredient list online if not on their product. They will tell you what grade of PG/VG they use, the percentages and the purity of nicotine but its very hard to determine what type of flavoring they are using, what type of sweetener (if any), type of preservative (if any). Certainly makes us much more educated abut what we are buying.
How many mg of nicotine you should use is subjective too- although rule of thumb and good starting place is to figure out the mgs by how many analogs you smoked, depending on how you smoked the mgs you try maybe too much for you. Many people find that to high a strength of nicotine makes them think of chemicals, although I never have heard 'soapy' associated with it, people taste things differently.
The recipe for e-juice sounds like a just a few things, the nicotine, the PG and or VG and the flavor. Although these are termed 'pure' that just means the grade they are and how much the chemicals and products used for making the component is cleared of things that were used (as well as any other impurities removed), not the they are made of any one compound. Except for the flavor, of course. While the resulting product is considered 'pure' to pharmaceutical standards, that does not mean they are 100% pure.
There is a very small (like 2%) part of the population that have taste buds and/or the ability to smell things the rest of us do not, just like there is a small percent that don't have certain ones and so things the rest of taste they cannot. An example of this are the people that cannot taste a type natural sweeter - to them it has no taste. The small percent of people that have receptors that react to things and 'taste' then often complain of a chemical taste as what the associate it with. So while its tasteless to most of the world, for a very few people there is really a taste to it and you can detect the very small, small amounts left behind that the rest of us cannot.
Flavor preparation itself can be a real offender when it comes to chemical or other odd tastes. They may use a pure fruit, even organically grown, or spice or whatever but the process of leeching and distillation or other processing the flavor can leave behind subtle things that most people are not sensitive to. Then you have these strictly artificial flavors that people often taste as more of a chemically flavor then or a natural one. You did not say what flavors you were trying but depending on the process used for tobacco flavoring some can be either chemically or leathery tasting. If you have always tried flavors with tobacco flavor mixed in you might want to try a non tobacco flavor. You might also want to stick with those juices with natural flavors instead of artificial or a mixture of both.
Then the sweetening - a lot of flavors have added sweetening because the PG/VG is not sweet enough for the taste of certain flavors or the flavor itself can be bitter. Although glucose can be found in some juices usually the sweetener is a non glucose or artificial type (will not raise blood sugar levels). As anyone knows, different people taste these sweeteners different, and experience everything from a normal sugary taste to a majorly chemical taste with very bad after tastes. Unless every brand you have tried uses the same sweetener this is probably not what is happening unless every type of sweetener you find bad tasting - in which case you need to find a brand that sweetens with glucose (sugar).
Preservatives: In most cases, even if the label lists ingredients of an e-juice the preservative is not listed, if some are used. I think this is because people associate preservatives with chemicals and they don't want people to start worrying they are vaping chemicals. Usually this preservative is citric acid, but there are pharmaceutical grade preservatives that are used. I have noticed that a lot of the larger brands that ship to retailers all over and their product requires a longer shelf life do use a preservative. Citric acid as a preservative is not the same as adding Vitamin C but its a very safe preservative used for a very long time but it could taste bad to some people. The downside of brands with preservatives is that people often complain of off tastes as most of these preservatives are not tasteless.
I don't know how long you have not been using analogs or how long you did before you started vaping. Has this always been the case for you or is it something you more noticeably reached? Taste and smell start coming back very quickly when you stop but as they do, and as they mature they decode smell and taste different. Some vapers may have noticed this when a same brand and flavor they liked and used a lot in the beginning all changes on them and they no longer like it as much. If you're very new to vaping it could be that from analogs your not tasting correctly and your taste and odor receptors are trying to put a tag on what they are tasting and missing it completely. If that's the case, it may just straighten itself out. You may also notice changes in taste and smell of other things too.
Now you can do a bit of testing - which might be easier and cheaper in the long run then going to multiple vendors in search of one that might have a juice without this taste for you. You can usually find all of these in 6 ml or even smaller samples so your not buying way more then you will ever need.
You might want to try a flavorless 0 mg nicotine juice (no added sweetener) and see if that taste you get is from the PG or VG or if it is tasteless to you and you don't smell anything. I would try the PG based first and then a 50-50 mix f PG/VG if you don't taste it in the 100% PG. If you are very sensitive to something in the PG, hopefully the VG will be tasteless to you, and you will know where the problem lies, and what options to pick when buying juice, more VG then PG or 100% VG if you can get it. If your chemical/soap flavor is detectable in the flavorless no matter whether its PG or VG or a mix you might want to contact the vendor and see what brand they use and then find a different one to try.
I would next try out sweetened flavorless 0 mg nicotine juice - not necessarily because you like it any sweeter then the PG gives it but since you don't know if a bit was added to what you have tried its a way to know if its the taste of the sweetener that is soapy. You can find 'flavorless' sweeter of the general types online at many e-juice vendors and just add a drop to your bottle of flavorless - and remember don't worry if it tastes too sweet - your not judging that but if that is where the bad taste is coming from.
If the PG/VG and flavor is tasteless, then you should try the same mix but with the nicotine in at the normal strength you have been using and see if its from the nicotine itself. If you find it here you may want to try a lower strength and see if that takes away the chemical taste. Its very possible that if it was tasteless without nicotine, a lower strength would not have that chem taste. I have read and seen many reviews that have mention 'chemically tasting' fruit flavors with higher nicotine strengths that tasted just fine at lower. I looked for there view and could not find it again on You Tube but the reviewer actually gagged on the review of a fruit flavor he got to review in his normal 224 mg strength but came back in a later review to say how good it was at a lower strength.
At this point you either have found your culprit or unflavored juice with nicotine and some extra sweetener is flavorless to you - as it should be actually, and hopefully, then it is the flavor used or possibly a preservative.
Next step is to get some flavor samples making sure you are buying from a vendor that makes their own, does not add any preservatives, not even citric acid. You may have to do a custom order to get the citric acid left out but if they are making to order that should not be a problem. You also want 100% natural flavors - which will limit flavors available because some can only be made from artificial flavorings or a mixture of both. I would also get a sample of one that does mix both but will leave out the citric acid and see if that preservative is your issue.
If you have to go custom made to get rid of this chemical/soapy taste, and I can't imagine vaping with that taste, you might want to consider DIY at this point and have complete control of what your putting in your juice and it costing you a great deal less then what you can buy even the cheapest juice out there.