Peeling gums, pain in jaw under teeth and flat ulcer

Hi, Don't know what's going on at the moment with my jaw- Had root canal on a tooth (2nd bicuspid on left) about 6mths ago- tooth now grey and trying to save for a crown. About 5 days ago, my gum directly under this tooth started to sting- I noticed it was peeling so I left it but it continued peeling on its own. This seems to have now turned in to a flat, white ulcer type thing that is quite sore. The following day I had a dull throbbing pain stretching from this area all the way back to the last molar- the pain feels like its located under the teeth (inside the jaw) and also along the outside of this gum adjacent to the lower portion of cheek. My gums do not look too bad- a bit dark red between a couple of these teeth- I have taken the precaution of flossing, gently brushing these teeth with pure tea tree oil (which is awful! but apparently helps with symptoms of gingivitis) followed by electric brushing with Sensodyne and using hydroperoxyl mouthwash -been doing this twice a day for three days. Symptoms seem very slightly better but yesterday, my whole bottom jaw on that side went numb which was very disturbing. Worrying I'm getting ONJ or something serious. I'm also on ritalin (have been for over a year) and last week put on Lomax for depression due to stress, so wondering if these could be issues. Any help would be great as I try to take care of my teeth and am still have issues with them.