I have brown discharge, it started a week after my period, and its been on and off for a week now.what is this?

my period ended on may 28th, then on june 2-3 i started having this dark brown discharge. it is very little, not like i need to change my tampon every few hours or anything...it stopped for a few days then picked back up, so its been nearly every day for almost a week. what could this be? ive been on new birth control since january, and this hasnt happend before.