I had one for 8 weeks and it drove me around the bend!!!! It was on my old tongue -
It was caused by irritation to the area. I think initially it been there for a while even before I discovered it. I think it was a hang around from rads to be honest where it was exposed to the incoming rads "beam" but over time and not being treated and continuous irritation it became painful so I noticed it.

Anyway of course I had a meltdown first. Had my SO's fellow look at it. He kinda blew me off saying it looked like I'd bitten it (not! it could rub on my teeth but impossible to bite that area). Anyway I went to my back up ENT and he said it looked like a very small canker (it was deep though) So he prescribed Oracort, and told me if it doesn't go away in a few weeks come back he'd do a biopsy.

I picked up the prescription a few days later, then started using it according to the directions (once a day at bedtime) It seemed to be healing but very slowly. So I changed my plan. Cleaned and rinsed my mouth after every meal (acidic foods etc... irritated it more) then I applied the oracort, it dries the area and forms a barrier. After a few weeks of this it was almost completely gone. Now it's fine. There was an area next to it more lateral on my tongue that was always sensitive. I had them file two molars in that area that were rubbing on my tongue (they rounded out any sharpened edges) and it healed as well. Since then things have been fine.

My tongue was reconstructed and sometimes swells it's already a little too big for my mouth with the flap, so when it swells it can really get irritated when I am eating and rubbing on it all the time.