Anna, is it inside of your mouth? When I think of "canker" sores, I think of fever blisters (on the outside). But I have had the ulcers inside of my mouth before and they are so painful!!! Fever blisters are equally painful and I have gotten a solution for those, called "Famvir", which is a very expensive prescription medication, taken at first notice, but it does the trick, for sure, within two days. I haven't had a mouth sore (inside) for years, for some reason, but I can remember being in so much pain, and in the "old" days, they used silver nitrate to kill the pain and it worked, but I don't think they do that anymore.

Hope you will be better soon.

Logan