WTF I bled?

Hi! So I'm concerned and kinda confused with my situation. So I have been a bit sexually active with my boyfriend recently. This last time that we had sex I slept over in his room and somehow bleed all over his sheets. My concern is that I don't know why or what caused me to bleed. It wasn't my first time but I haven't had sex very much because for some reason my vagina is extremely tight. It's so tight that the first couple of times I had sex it hurt too much to actually go all the way. Now this last time I was fully into it and I'm not sure why I would have bled. One reason I think I might have bled is that at one point my boyfriend was fingering me and I did feel some pain but it went away quickly. Could this be the explanation? I'm concerned and wonder if this has happened to anyone else?