I Got A Root Canal Done On The Bottom Right

I got a root canal done on the bottom right molar tooth. Right that evening I started to get little white bubbles on my right side of the tongue. I informed my doctor and he said they would go away. After about 2 weeks they went away and then I had this big bubble under my tongue. It is really big now. I have seen the same dentist twice now and he's prescribed me antibiotics for 1 week as well as ruptured it a little bit. But, it's not going away. Last week I saw another dentist and he prescribed me steriods for a week. I have completed all my medicine courses and now that bubble is very huge. I can't speak properly and it pains when I eat or even swallow my saliva.