Small Bump Behind Teeth, Inside of Chin

Hello,

I have a small soft bump that keeps popping up in the area behind the teeth -- almost where the mouth floor meets the right side of my mouth -- way below tooth 30, I think (it's right near some sort of bone). I can't actually see anything, but I can feel it with my tongue -- when I gently push up against it with my tongue, it will disappear for a bit but then come back. Occasionally, when I push up against it with my tongue and then immediately spit out, there will be a fleck of skin (or whatever the mouth equivalent of skin is) and maybe an occasional spot of blood.

Could this be a dental fistula by any chance? I know fistulas typically appear on the gums, but could one have made it down this far on the other side of my teeth? If not, anyone have any idea as to what it could be?

The reason I ask about a fistula is because I had a root canal on #31 about five years ago which was done improperly. I had a fistula tract (possibly for years) on the gums, and had a root canal retreatment a few months ago. The fistula tract disappeared with treatment. This bump in my mouth appeared a couple of weeks ago, so now I'm worried it may be a dental fistula and I'll have to get #31 pulled. Any thoughts?

Thanks for your help!