"Period" came a week early while on BC

Melissa
Hey ladies! Just curious if any of you have had this happen or know why it would happened. My period isn't due for almost a week, but today it seems it has started. I have light cramping and bleeding (dark brown blood) it's not very heavy but not spotting either. I am on birth control (Alesse 28) and have been on it for a few years. I haven't missed any pills and I take them exactly the same time everyday. Technically I shouldn't have started my period since I'm not on the sugar pills so I'm very confused! Any help is appreciated! Thanks! 😊