Try different types of liquid refills. Some people are intolerant to different base materials or to different flavorings.
For example VG is sometimes a culprit because it can be made in different ways, some people finding that one of those types is not suitable for them. Flavorings can also produce a similar result.
You'll need to get some different types/makes of liquid, and trial them. Some people seem to be able to consume huge quantities of just about anything with no effects at all - others have to be selective. Some even have to use unflavored base, or a known 'hypoallergenic' type produced in a lab.