Cramping during and after sex?

Sevina
Yesterday me and my boyfriend were having rough sex. We were doing a few positions that allowed him to go deeper than usual and after I orgasmed I started having really intense pains like I was cramping whenever he went too deep. He eventually finished and the pains calmed after about an hour or so. I was wondering if anyone knows who could've caused this? 
I am on birth control (the Mirena IUD) and my boyfriend also said there was a little blood on the condom when he took it off before he came inside me.