Please, please help me. blister or callus on right armpit?

Okay, so it all started out with scoliosis (curvature of the spine) and having to wear a soft brace. that started in august, 2005 to may, 2007. It was a brace called spinecor that had several straps that went all around my back and under my armpit. It seemed the more I wore it, the more irritating the blister got under my armpit. Unfortunately the brace did not work and I had spinal fusion in September, 2007. Problem is I STILL HAVE THE BLISTER. It's been since may of 07 since my brace and I thought time would heal it. I don't shave under there and i put deodorant below it and it is still irritating. It's just a lump probably a little smaller than a dime. It hurts when I touch it too. It won't go away. Please, I'm begging someone to tell me what this is. Is it a callus, blister, wart? Yeah I know I should go to a doctor but who...dermatologist? Please don't just say "duh, see a doctor". Please give me specific details. Will they have to perform surgery on it or cut it off? I'm not popping it! it hurts like he**. Is there any over-the-counter medicine I can take? Like a cream or something? I have no idea what it is! I mean it isn't waking me up in the middle of the night or anything but it's irritating me sometimes in the day. And it's annoying because I really want to shave there and put deodorant on. You could see it if I put my arms up, too. All answers are gladly appreciated. Please help me. I want to figure out what this is. Thanks so much.