Oh god ... I could write a book about canker sores....
I have had hundreds (thousands?) of the little buggers.
There was a phase for about a year and a half where I had two or three at a time, all the time. It was so bad that I was pretty convinced, in the context of a couple of other things, that I had a disorder called Crohn's Disease that causes bowel problems, but often also causes canker sores (since the tissue in our mouths and on our tongues is the same as that throughout our intestinal tract). I had a GI doctor that was also suspicious enough to do a ton of tests (ouch

) to figure out what was going on. There was also suspicion of Celiac Disease, which can also cause mouth sores
What happened is that everything came back clear. And it was a total puzzle until I started getting effectively treated for my sleep apnea and anemia and they almost completely went away.
Turns out they flare up when the immune system goes to pot because of any number of chronic conditions. Anemia also specifically disrupts the membrane on the tongue.
Bottom line -- make sure there isn't something else going on that could be dampening your immune system. And make sure you are not anemic due to iron deficiency, because that is often a culprit.
Outside of immune system stuff, there are some things I came across while doing a ton of research about canker sores when I was so miserable because of them. A lot of people have them triggered through citrus foods; also, there is a substance in most toothpastes that can be very bad for some people (I think it's called sodium lauryl sulfate) because it is slightly abrasive (like citrus fruits, it disrupts the membrane on the tongue)
A lot of people also put baking soda, salt, hydrogen peroxide, or alum on their tongues and claim it gives some relief. All of them work by leaching moisture out of the sore and (maybe) helping it heal faster. I never found that those things worked much, but you could try them.
Good luck!
Did I say I could write a book ...
