Plan B pill messing up cycle?

Ok.. So my bf and I had a little mishap on my first day of my period 8 days ago.. I know it's basically impossible to get pregnant on your period but I went ahead just to be safe and took a plan b pill anyways.. That next day (2nd day of period) I was still bleeding normal.. But the 3-4-5 day i did not bleed at all.. Then the 6-7-8 day it's like it's basically started over and I'm bleeding again!! Has this happened to anyone before? What's it mean? Help!