I've had this reoccurring canker sore on the center of the inside of my lower lip. It usually looks and feels like a small hard blister or pimple, filled with liquid or puss and is usually gray in color. It usually pops up whenever im stressed but sometimes at random too and can be slightly annoying in pain. As of now it is an open sore (must have bit it last night as I slept) with a white ring around it (dead skin?). Anything I can do to get this away? Ive had it for months.