I bled?!?!

So last night I had sex with my boyfriend and I slept over. Somehow I bled all over his sheets. I'm not a virgin but I haven't had a lot of sex before. The first couple of times I had sex, I had to stop because it hurt too much because I was too tight . Last night I didn't have to stop, everything felt good but somehow I bled. I think the reason I might have bled was because at one point he was fingering me and I did feel some pain but it went away quickly. Is this possible? Neither of us felt anything but he says that there was a lot of blood before he washed his sheets. Has this happened to anyone else and if so was there a lot of blood?