I'm not sure if this is classed as an allergy, but there are definitely reactions to something. I had to stop PG, very sore throat, awful cough, which was disturbing, I quit tobacco cigarettes coughing my head off!, lung pains, both sides, and a general feeling of being strangled from the inside out!
I switch to pure VG, and have had no problems at all. One cartful of PG will put me right back on the disabled list, so has to be something to it.
We all need to drink more water, but water won't stop the kind of reactions you talk about. Switch to a good verified Vegetable Glycerin, such as ECOpure and give it a try. I try to stay away from generic Glycerin because source of ingredients can be questionable, it could be "synthetic" or could be animal fat or vegetable.