Vendors of VG liquids have generally thinned them down to a usable viscosity. If you buy VG base though, it may well come at the original viscosity and be far too thick to use. As it needs thinning by about 20%, you must order it much stronger than your designed end result.
If you think you have an intolerance to either PG or VG then try buying unflavored base from two different vendors (so if one has an issue, at least you have a comparison). Decant 2ml into a 5ml dropper bottle, and take it close to the final nic strength you want by adding distilled water, if required. The easiest way to get distilled water if you can't buy it locally (it's battery water from a gas station, by the way) is to scrape the ice off the inside of your freezer - this is distilled water.
Vape some by dripping it directly on to a clean atomizer. You should be able to taste the raw material strongly, although every base tastes different and has different characteristics. Now you know what the unflavored material tastes like, add a few drops of a simple flavor to mask that taste. You are aiming for the minimum. As 1ml is about 22 drops from an average dropper, and you have 2ml, then adding 3 drops of (say) caramel will be about 7%. That should be enough to mask the original flavor, but try it - it could need more, depending on the strength of the flavoring. Some people can get away with less.
When you have a satisfactory minimum-flavor liquid, make a lot of it, and use it exclusively. You'll know in 4 days if it is problematic or not. If not, then add more/other flavors. If you have any issues you'll know what did it.
It's not a bad idea to add a couple percent of PG even to all-VG mixes, the powerful bactericidal and virucidal properties can't do any harm. After stage 1 in the above process, it's easy to find out if this causes any problems for you.
Note
Every '100% VG' e-liquid has been thinned down about 20% either with distilled water or flavorings. DW is the normal material. Therefore 100% VG is of course a misnomer. Watch out that the flavorings were probably based around either PG or alcohol, maybe you don't want that.
There might be some thick VG finished e-liquids out there, they won't work too well in regular carto tanks most likely - you'd need more/bigger feeder holes.