I took an emergency contraceptive and i had my period it lasted for five days , it was heavy. now that my period is due i have dark brown discharge.

Plan B: plan B can cause some irregular bleeding and not all bleeding is your period, so check a pregnancy test just to be certain. Some cervical infections can also cause a brown discharge. Probably time to see your family practice doctor or a gyn and get an STD screen and talk about using some birth control as plan B isn't a good regular way to prevent pregnancy.