I've Been On The Pill For Over A Year And

I've been on the pill for over a year and take it consecutively. Always had a period during the allotted time and very minimal symptoms such as cramping etc. I'm not scheduled to start my period for another 2.5 weeks and I'm having severe cramping and a light period for a few days now. I am in a monogamous relationship but we are sexually active. Any idea what could be causing this?