I have a blister on the outside of my upper gum, in the back of my mouth. I think it has been there for two or three months -- I thought it was trapped food at first that I couldn't dislodge -- and in the last day or so it has gotten bigger, to the point that I examined it and noticed the blister. I poked it with a sterilized needle last night, and no pus came out of it, just a little blood. The odd thing is that it doesn't hurt now and has never hurt. Can someone tell me what it is and what I should do about it? Should I try saltwater rinses?