Brown/pink vaginal discharge 4-5 days before period, on mononessa, is it implantation bleeding

Hi, my boyfriend and I were stupid had sex about 2 and a half weeks ago, we were unprotected but he didn't cum inside me, I had taken the Plan B pill three days before that and I started birth control that day. I am no having vaginal discharge that is brown/pink in color. I should start my period 4-5 days, is this implantation bleeding? Or is it because of my birth control? I take Mononessa