I had a yeast infection and i took the one day treatment and i felt completely fine. but i had sex with my boyfriend and it still hurt so bad. why?

Yeast infection: Even though the yeast infection may have resolved after taking the medication, you may still have had some inflammation going on from the infection itself. Probably best to wait a few days before having sex. If it continues to hurt, you should see your gynecologist to be sure you don't also have a different kind of infection like an STD or bacterial vaginosis.