Originally posted by: JulesMaximus
It's probably a canker sore. Fairly common actually, try rinsing with some Colgate oral rinse or Orabase applied directly to the sore.
I've had them on and off my entire life but stress and eating foods highly acidic tend to bring them on more than anything.
Agreed. That's what it sounds like. I envy the OP for not knowing what this sort of thing is. I've got three right now.
Get one on one cheek from biting it while chewing. Shift to the other side, and then bit that one. Then my tongue, while it's trying to carefully shuffle food around so as to avoid causing additional pain, manages to get in the way, and it also gets bit. I use Orajel, but it wears off after about a minute of eating. I think I need a permanent prescription for novocaine.
It might be hereditary. My dad had mouth ulcers for a long time. His cure - he turned 40, and they just about stopped completely. Other than age, nothing helped.