Why am i 3 days late for my period when i take birth control? what does this mean?

Pill regulates cycle: The pill creates its own chemical environment- and is the dominant factor regulating your menses, while taking it. If your pill is one that has an extended cycle - like a 24 or 26 day pack, then you may experience a slight delay in the onset of your cycle, when compared to your natural menstrual pattern. Generally these extended pill packs offer a shorter and lighter flow. Good luck.