To my fellow vapers, do experience mouth sore? if yes here's my 2 cents suggestion, viz:
Use toothpaste without SLS (Sodium Lauryl Sulfate)
gargle often if possible (warm water with a little salt will do)
take vitamin B12
Vaping do cause dry mouth and dry mouth usually lead to mouth sore. In addition thereto, quitting smoking can also lead to sore mouth.