Brown spotting every day since taking Plan B

I took Plan B a month and a half ago and have not been sexually active since. pregnancy test came back negative. Every day I’ve experienced brown discharge (I’ve had this in the past and been told it’s old blood but never every day).

Sometimes there will be some light pink spotting or the tiniest amount of red blood. A couple of times there’s been dark brown clumps/clots. I’m 22 and never in my life taken birth control besides that one emergency contraceptive pill. Does anybody know why this could be? :(