Random bleeding

So I have no idea what happened to me but about a week ago I was laying in bed with my boyfriend and he noticed I was bleeding from my private area and he freaked out but I had gotten off my period like the week before that so it couldn't have been my period but It lasted maybe 5 hours and then went away when I went pee there was no blood in the toilet just little particle pieces like tissue from my vagina I didn't wanna tell my mom because me and my boyfriend had sex like the day after my period ... What could it have been ? Someone told me I might of had a miscarriage but is that even possible to be pregnant that fast and then lose it within the same week ?