please help

so i had a CP (i just marked it as my last period on the app) but since last sunday i started my birth control. i treated the CP just like a normal period and everything went fine. i’ve had regular white discharge since, and now i’m on my second fertile day and i have the rather dark brown blood and it almost like a light period. could this just be old blood extracting or an odd spotting side affect from the pill? help please.