Brown period blood?

Three weeks ago I took a plan b and this is the time my period was estimated to come. Two days ago I was spotting and yesterday I was fully bleeding so I’m assuming I got my period and wore a pad. But when I looked at it, all of it was completely brown. It was a lot of blood like usual but just brown. I have all the period symptoms, heavy cramping, tenderness around the breast and nausea. Btw I’m not on any birth control . Not sure if this is something normal or someone has experienced this