i have the same thing! Did you ever figure out the problem?
you need to see a physician, you may have something going on with you.
let your doctor know your exposure so that he can order the correct test, hiv and std's. even though you had heterosexual relations and is considered low risk, not low enough to not test. and yours was anal considered high risk.
you need to ask your boyfriend if he has std's, or hiv, and possibly get tested together. good luck.
my boyfriend and i have never had sexual relations with anyone else before. that's why im not sure if it is an STD or not