If it is a sore/cankersore and of you can stand it, drink Buttermilk. Also, before swallowing let the Buttermilk sit in mouth over where sore is. I am not a doctor but I do know via experience.
Doing the above can and has (for me) cleared up sore/canker sore in a day's time.
Cultured Buttermilk (found at your local grocer) has live cultures which are basically good bacteria hence assisting in healing process. Good luck! Hold your nose when drinking Buttermilk!