Stomach pain straight after sex and day after!? what is it!?

I have been on my period since lasts Sunday and started taking pill since Saturday and yesterday I had no blood at all so me and my boyfriend had sex yesterday and he pulls out so obvs I was cleaning up making sure nothing in me and there was a line of red blood but then I've had no more blood since but ever since immediately after sex I've had a really painful belly since sex yesterday night and still got in now - I'm worried