Confusion??

So I last got my period January 16th, today is now March 3, so obviously i missed my period by over 2 weeks.. however yesterday i started bleeding.. it was fine.. was relieved i finally got it.. BUT today, i wake up and my period blood is almost Black & i’m cramping soooo bad (i never really get cramps) Its light in thickness, like almost water-like but it was a lot. I had to completely change. Could this be just old blood coming out after all that time, or something linked to pregnancy or loss of?