What Causes Light Vaginal Bleeding After Intercourse?

i am a 19yr old female 5'7 160lbs i have had my period 2x this month i had one that was 4 days long and a normal flow i had intercourse 2 days later then again bout a week after with my boyfriend. after the last time we had ibtercourse i started bleeding a very ligh,bright red and its been going on for 4 days and im worried i am also on birthcontrol.