period lasting too long

Emily • 17 and from NYC

so i got my period last saturday after my boyfriend and i had sex. it was a week early and it was all brown for the first 3/4 days and for the last couple of days it's been red but it's been a lot and then very small. like i'm wearing a panty liner and that's all that comes out. i have never had a period that has lasted this long. i'm starting bc for my first month so maybe it's that? but i dont know why it's lasting so long, can anyone help me??