help meee

I ended my last period on the 27th of December and started in birth control for the first time on the 8th of this month.
I've been diligent about taking it, and take it at the same general time everyday so I figured I was set.
Last night I let my bf cum inside of me, and this morning I woke up bleeding and cramping.
My period is a week early and I thought I wasn't supposed to get it?
I don't know, is this all normal?
Thanks!