What is the ohm (resistance) rating of your coils? Low resistance coils can cause a harsh, hot vape to sensitive vapers. Higher resistance coils (2.0 - 3.0 ohm) can provide a cooler vape.
Be sure to drink PLENTY of water. Pg & Vg both draw moisture from the mouth, causing dry mouth, and it must be replaced to avoid dehydration.
Biotine is advertised to help with dry mouth. Try that.