The next day after having unprotected sex i started to discharge and it was brown. what does that mean. i have been on birth control pills for 3 month?

Probably normal: Most likely your cervix bled a little during sex and the blood came out as brown discharge. Make sure you are getting routine exams by a gynecologist, including pap smears and STD screening.

Blood: It's usually your normal vaginal secretions mixed with blood. Maybe your period is coming, or break through bleeding, or traumatic from sex itself. What's important is that you have been check for disease that are transmitted sexually and HPV via a pap. If not do so. If yes and you trust your partner. I would not worry unless it continues