Bloody sex?

So my period ended a few days ago and me and my boyfriend had protected sex the day after it finished. We had sex again 2 days later. We began without a condom but he put one on when I said I wanted to be on top. Everything was going fine when he suddenly stops me and tells me I’m bleeding. I didn’t feel any pain but there was a lot of blood. I went to check it out in the bathroom and started to get really bad stomach cramps. Do you ladies have any idea what this might be?

I should also probably say that I am on the pill.