WHY AM I STILL ON MY PERIOD????!!!

Zoe
I had pretty much finished my period on Saturday with just really light spotting here and there left. And I was sexually active Saturday. Neither of these circumstances are new to me or my body. But during sex I began bleeding again, so much that I bled on him a little. I was mortified, it was my first time with this particular guy. He convinced me it was no big deal. And I popped a light tampon in and we went to sleep and everything was fine. But now all day Sunday and today (Monday) I've been bleeding consistently. It's been very light but also none stop. This has never happened to me before. Also it's very dark brown. So dark it's almost black. I don't know if this is normal? I'm kind of freaked out.