It's a canker sore - nothing to worry about! I don't think people know exactly why canker sores appear, but they are not contagious. You will get them inside your cheeks or under your tongue if you by mistake bite down hard on them. I've heard that you may also get them due to a lack of vitamin C.
Take some pain reliever as I know they can be quite irritating (especially when eating). I always use Anbesol to temporarily numb the area. Then I drink lots of orange juice and suck on zinc lozenges. My boyfriend rinses with with salt water. My mother dumps salt directly onto the sore (super painful!).
Canker sores have nothing to do with how well your mouth hygiene is. Doctors don't know how to prevent them, but maybe your doctor can prescribe some medication to help ease the pain. Other than that, you just have to wait for it to go away (usually takes about a week) and in the meantime, don't eat anything that will irritate it (spicy, salty, acidic).
Oh... I see you say you've had it for two months. They're not supposed to last that long. You better make an appointment with a doctor.
[This message has been edited by noelwr (edited 10-02-2003).]