mystery mouth problems

My little mystery ailment kiddo is at it again. He's been teething for the past 3 weeks....started with hand in the mouth and drooling like a baby again, low grade temps and generally miserable. Then the mouth sores started. It was one little spot on his right corner of his mouth. Then it went crazy. The only way I can describe it is canker sores on steroids.  It. was. alarming. He bites them and they bled, her cries and doesn't sleep at night:( Double :(:( SO this prompted a trip to the Ped. He didn't think it looked like anything they typically see like hand foot mouth, thrush, etc. So he swabbed it and gave us and Rx for the magic mouthwash. Good luck with that on a 2 year old. I just so happen to be taking the girls to the dentist the next day so I called to ask if Henry could be seen too.  The dentist thinks it's a burn.  She actually asked if we had any corroded batteries he could have gotten a hold of? Um, yah, no. I let her talk, but I know he did not suck on or ingest a battery. The sores have since migrated over his lip and are now onto his upper lip. It's terrible,  He looks awful and on top of all of that he got a terrible cold/cough. Por kid can't catch a break. I'm hoping it will run it's course, and that is is "just" canker sores since that's the only thing anyone can deduct from it. My poor little dude:(