I have been on the pill for about 6 years, and I am currently on a 13 week cycle (have been for about 4 years). I started taking the sugar pills for this cycle on Sunday and have noticed menstrual cramping the past 2 days (Monday and Tuesday), but there is no blood. It normally tastes a couple of days for my period to start, but I have never had menstrual cramping before hand. 

Does anyone know what could be the cause of this?