reflux is often caused by over filling devices so that droplets of the juice go into your mouth. It can also be caused by the flavour or base you are using. Some people prefer VG, some people prefer PG. You need to experiment a bit.
It is not the cheapest, and neither does it have much taste, but you could try some ecopure from intellicig. It is really just VG and nicotine in the regular stuff, but if reflux is really a problem I would suggest trying it and making sure you are not over filling.
Also the cotton bud is a friend to the vaper. Although the buds on them need a bit of manipulating they can really help get rid of excess moisture around the inside of a mouth piece / drip tip, threads attys ect.
Sometimes when we use one flavour, and then switch to another, the flavours can mix on the heads if there was still juice on it. This can also sometimes cause a jump in sourness or acidity levels, it usually wears off after a bit of juice has gone through it. Sometimes some juices can get stronger in the tank systems as we vape. It might be worth tipping the old juice out when filling it up occasionally as constant topping up can cause a bit of a build up of flavour in the tank. So refreshing the juice every so often rather than just topping it up every single time might help.