Mouth burning when eating?

You know that bit of extra skin inside the corner of your mouth that people like to bite sometimes? Well, I bit down on it quite a lot after getting into a habit of it, and it got pretty swollen and chewed up very bad. But this one is different, when I eat anything acidic, (e.g. Apples, oranges, ketchup, mustard, pickles, tomato sauce) I will experience the most awful burning pain when it comes in contact with that part I chewed up, and it makes it hard to eat anything. I never noticed how salty or acidic our day-to-day foods were until now (yes, salt hurts it very bad too, as well as soda). So i know the culprit, but I wonder if you guys have any suggestions on how to help it? Or will i just have to let it heal?