What Causes Brownish Vaginal Discharge And Diarrhea?

I had my period last week, then had unprotected sex and shortly there after I had a brownish discharge. At first I figured it was just old blood since it occured quite quickly after my period. However, the discharge has kept up for the past couple days and it has now been a week and today I started having diarrhea! What is wrong? Is this normal?