HI there... sorry you're going throught this again. I had a similar sore that caused me pain I noticed it on a friday after eating out. Then had the usual panic attack over it. I called that monday and asked for an appointment with my SO (who I trust) I figured it would be a two week wait to get in - if it was gone by then then great... but if it was still there then I would have a valid concern and it would be dealt with (let me tell you it was painful) -well I was wrong. Firstly I got in two days later which was great but I didn't see my SO just his fellow who I don't know at all and definitely don't trust particularly because he blew me off saying it was likely an ulcer or injury from having bitten it... NOT.. the location was all wrong for a bite so then I made an appointment with my local back up ENT and had to wait two weeks. When I finally saw him he said it was very small didn't look like anything he would be concerned with. Thought it was an ulcer. Prescribed Oracort and told me to apply it as directed then come back if it didn't heal in two weeks. I did as recommended and used it as directed which was once at night... didn't help much though it seemed to get better slowly. Since it seemed to be improving I took another tact...(he had said he would biopsy it if it didn't improve) I brushed my teeth after each meal, rinsed my mouth to too, applied the oracort and stuck to NON irritating foods... soft - non acidic - basically. it took 4 darn weeks to heal!! but it worked.

Right now your mouth is still damaged from radiation. any cuts or injuries or spicy and acidic food can really hurt like the devil (and cause ulcerations). Try keeping the area super clean, and be gentle with it.
It may take a long while to heal but it will. Mine looked small, but the deep part was small. it had to heal from the inside out by the time it did it had to have been about 4mm long. I still get irritation and sore patches from eating and I'm almost 19 mos out of treatment etc.

Hopefully it's nothing. I am like you - not super sensitive to pain but mouh sores can hurt like the devil.

YOu're dr. was right though...based on your history better safe than sorry.hugs...