I need help.....ASAP

So there’s this guy I’ve been on and off with for almost a year, and I’m, we haven’t dated, I would just call it “fuck buddies” type thing. So uh, today I went over there and you know we did our thing, but I had realized halfway through that I was bleeding!! And ladies this wasn’t a “spotting” situation either. He noticed, got me something to clean up with. But god, the blood was E V E R Y W H E R E. This was the most I’ve ever bled in my entire life. Not even my period was this heavy. So I know my period is coming because my body has been telling me that, but ever since we had sex I haven’t bled again...it’s weird but I want to know whats wrong😕 someone please help I’m only 18