What Causes Brown Vaginal Discharge After Taking Unwanted 72 Followed By Sex?

I had sex on 7 n 8 day of the cycle and also took unwanted 72 within 48 hr. I didn't had any side effect of med. But now I m having brown discharge since 15 day of cycle. Today is 22 day n discharge has not stopped yet. M I pregnant? Or do u gave got any infection? What could be the reason for discharge?.. Plz reply in detail I m a medical student