What Causes Missed Periods While On Cerazette?

Hi, I have been on Cerazette for 3 years now, never missed a pill, always take it at the same time. I had some heavy bleeding at the begining, but haven't had any periods in about two years now. However at the moment i am experimenting intense thirst, I'm constantly thirsty, have got bad winds and I've noticed that I'm more sensitive to smells... I have been with my partner for a year and a half and we don't use condoms anymore. I am a bit worried, could I be pregnant?