I am on birth control pills, the 3 week one so i don't have the placebos week so i'm not supposed to get my period. I've been on the pills for four months now. i never miss a pill or take it late. i got my period the 16th and it has yet to stop. is this normal or should i be concerned? The blood flow is always changing everyday. a couple hours it's light and then another couple hours it's dark reddish brown and it just keeps switching back and forth.