Wait... Apthus ulcer, canker sore, cold sore...All the same. They can result from stress, fatigue or just because they want to. There is no cure but if you get them often then you can take some medicine (acyclovir) to lessen the life or ease their pain. For the most part they just have to run their course. If you don't do anything they are gone in 14 days or so. Watch spicy or acidic foods.
Check with Doc. Check with your doc. That is what he/she is trained for.