Period need help!!

A few weeks ago I took plan b after protected sex. I got a pd week early. During that pd I started bc back up but only took three days worth. Five days later I got another pd but much dark almost black blood. Now a few weeks later during the time I should have another pd I have this. Obviously my body is thrown off but is this my period or is it about to start? I have mild cramps with it to. This is day three of it