What Causes Stomach Cramps And Vaginal Bleeding After Periods?

Hi i missed my period last month and i am on the pill. Then a week and a half later i took a pregnancy test and it was negative, maybe 2 days later i started having cramps so i thought it was my period then a weird reddish brown discharge started. Now maybe 2 weeks later i am cramping and bleeding. Any suggestions on this because idk what is going on?