Can someone plz help me..?

I just got off my period 3 days ago (today will make the 3rd day), and it was 5 days long (my period).

Since the day I got off, I've Been having a good bit of cramps. I had sex 3 days ago, and I know IT'S WAY to early to tell if im pregnant, as I don't think I've even ovulated yet.. I just want to know why I'm having cramps pretty bad after my period ended?