What Causes Brown Vaginal Discharge And Abdominal Pain After Having Intercourse?

a week ago today i had unprotected sex, i went straight to the chemist the next morning to get the morning after pill. ive had thrush since before i had the unprotected sex, which i still have now and am treating accordingly. however today i have had a light brown watery discharge, and feel like i may be getting a slight abdominal ache. im worried sick and cant get an appt at my doctors or gum clinic until thursday. it sounds very much like and STD, but i wouldnt know what.