First off, HOORAY for you for nursing so long!!
I went down this road with my daughter. She had EIGHT teeth at the time. She bit so hard she broke the skin, it got infected and I ended up on antibiotics. We nursed through it, and we broke her biting habit.
My daughter would bite, and I would end feedings, just like every one suggests. Well my little smarty pants put two and two together that every time she bit me the feeding would stop. SO, when SHE was done nursing without warning she would bite me. I would stop the feeding, and she would get down and go play. She is such a freshy. lol
Well, I realized that I was just nursing her too much. She was getting older and eating solids. She wasnt interested in nursing as much as she once was. I cut her feedings down, and I let her initiate the nursing sessions. I would sit on the couch and put her in my lap to see if she was interested in nursing. As soon as I did that, she stopped biting.