So about 2 weeks ago I let my boyfriend cum inside me, I was on my period. I told him it wasn't that common for a girl to get pregnant while on their period. Did I make a mistake???

Well, yesterday I noticed that I was bleeding down there, but I'm not supposed to start my period for another week. My period is never early, I don't get it. And it wasn't even like full on period blood. It's like spotting, I've never spotted before and I'm 21 years old. It's kinda scary. Any advise???