Confused

Okay so my period ended on Dec 30 and on Dec 31 I had unprotected sex. On January 2nd my SO got me a plan b that I took first thing that morning (didn’t take it the first as he went to a bunch of stores and most were either closed or didn’t have any) well I woke up today and felt wet when I went to the bathroom and checked I had a bunch of blood in my underwear I assumed that unfortunately my period is starting again but what is confusing me is that when I wipe it’s all brown and not red. No it is not discharge. Has anyone had this happen before?