Is Pregnancy Possible If Cerazette Is Continued?

Hi,
My son is now 25months old.I had to stop breastfeeding him after he turned 12months old as he never took it.I have been on cerazzette pills as prescribed by my OBGYN for more than a year and half. I havent got my regular periods yet...my concern is are there any chances of pregnancy if i continue with cerazzette.i had missed the tab for 3 days in b/w but considered other precautions(abstinence for a week) and then continued the normal routine.
Thanks for your response and time.
Ann