Just got my period 6 weeks postpartum??

Hi ladies, I had a c section 6 weeks ago today. Stopped bleeding vaginally around 4 weeks- it just slowly tapered off. Then all of the sudden yesterday I start bleeding! Not even bloody discharge, straight blood. Called my OB and they said because I’m cramping it’s most likely my period. But I’m exclusively breastfeeding so I’m very confused? Started the mini pill (birth control) a week ago so that’s also a factor. Anyone have any insight or experience with this???