For years I had these--ask you dentist for a prescription for Kenalog in Orabase, touch the sores with this the minute you feel one developing, (it comes in a little tube and can dry out once opened, so keep extras handy), they are more expensive now--at that time $2.00.
Sometimes rinsing your mouth with Milk of Magnesia helps--some feel acid causes these, don't drink orange juice or eat tomatoes when this happens, and rinse mouth with salt water,
I have used liquid Echinacea on these and fever blisters--this can help but is diluted in the mouth,
Your dentist can touch these with silver nitrate,
or last: I recently read where a liquorice patch will help these and they get well several days faster. I have never tried this, but my housekeeper claimed her Mother in Bastrop used to give her liquorice root. I googled this--see under medicinal purposes..interesting.
Some things seem to work at different times..just get to them at the first sign. Stress can also aggravate these--I use to call them 'stomach ulcers'--why I don't know. They started for me about the age of 10, through college, work, etc. I am now retired and only seem to get these now if I bite my lip or inside of mouth. A lot of trial and error. A physician friend suggested the Kenalog. The prescription Kenalog in orabase has cortizone and really worked. Good luck, Mary