so embarrassing!

So me and my boyfriend had sex last night and I guess when I left there was blood all over his sheets. Not like a murder scene or anything but like you can tell there was blood. He snap chatted me it and said I left a mess. I feel so embarrassed but more importantly I have no idea where the blood even came from! And i know I'm not on my period. Could it be because I was dry when we were having sex?