Plan B

My boyfriend and i were so reckless last Sunday. He came in me. I had just gotten off my period when it happened and after we were done we went the CVS to buy a Plan B pill because even though we could support a child, we aren't ready for one just yet. Anyways, i took the pill right away. Just this past weekend on Saturday i started what i believe to be my period? When i should've started towards the end of this month. It was pretty heavily the first day when I'm used to the second day being really heavy. Then it continued with dark brownish discharge. Is that normal? I know the pill throws your period off and stuff, but I just want to make sure I'm good. You know? Haha. Thanks in advance!