How Can A Period Despite Being On Seasonique Birth Control Be Stopped?

I am 23 years old and on seasonique birthcontrol. I am not supposed to have a period for another month or so, but have been having a period for the last 2 weeks. I am lightheaded and have a constant headache now. I've also just started experiencing cramps (which I've never had before). What could be going on? And how do I make my period stop?