Watery blood??

Ab

So me and my boyfriend had sex yesterday night, and he finished inside of me like always, and i was laying there afterwards talking when all of a sudden I feel a bunch of liquid fall out of me, I get up to go to the bathroom figuring it was his semen leaking out, but it was blood, light red and super watery it was dripping out like water out of a faucet.

This has never happened to me!? what could it be??