It sounds like you could have herpes, which is an *extremely* common disease in the human population--about 1 in 4 people have it. You can get it from sharing drinks, from oral sex, or even from kissing Grandma; it's a very successful little virus.
More info on herpes: STI File: Herpes Simplex
To find out if that's what you've got, and to get suppressive and symptomatic treatment, you need to see a doctor while you've got an active sore. They can test it and find out what's going on with you.
(It could be something else, too--which is why it's important to see a doc.)
"There is a tragic flaw in our precious Constitution, and I don’t know what can be done to fix it. This is it: Only nut cases want to be president." - Kurt Vonnegut, "Cold Turkey"