What Causes Heavy Brown Discharge, Cramps And Diarrhea During Periods?

horrible painful cramps for about 15 hours straight, heavy brown discharge w/ some blood, and diarrhea. All of this happened at the time of my period. I had sex for the first time in 6 months about two weeks ago. Could i be pregnant? I know brown discharge is sometimes a sign of pregnancy, but since it was so heavy i didn't think it could be