It's possible to develop an allergy anytime. About 10% of people are allergic to PG or VG. Some find either one an irritant - that's the case for me and VG.
Try some unflavored pg nic and some unflavored vg nic. If either causes a reaction you'll know what it is. If neither one does, try adding some flavoring. It could be VG, PG, or Flavoring that's the culprit.
Edit: A member reported developing a reaction to banana flavoring.