I've been having the same problem, and also I have ringing in my ears, and now can't hear frequencies above 8-9k. Did some reading, and it seems that PG may be toxic to ears:
The PG in e-cigarettes can cause hearing problems. A caution to those who may experience symptoms. • r/electronic_cigarette
The PG in e-cigarettes can cause hearing problems. A caution to those who may experience symptoms. • r/electronic_cigarette