I have had my period for 11 years now-always a 30 day, on the dot cycle. I have been on birth control (the same brand) for 3 years now. The birth control never made my periods lighter or shorter as it does to other women, I normally have 5-6 days of moderate/heavy, bright red bleeding that gets darker and tapers off during the last 24 hours of my period. Suddenly 4 months ago (and every month since then) my period has come 1-2 days later than my normal on the placebo pills and has been 3 days of light flow, dark brown/black blood from start to finish. What could cause this change and is it something to worry about?

Have you talked to your doctor about this? He/she can give you the info you are looking for.

We can't diagnose you on the internet, no one can, not even a doctor.

Go to your doctor.