What Causes Abnormal Vaginal Discharge While On Cerazette Tablet?

Hi, I have been on Cerazette for almost 2 years now and every so often I get some brown discharge as I occasionally forget to take it at the same time every evening. However for the last couple of weeks I have had brown discharge and more recently severe stomach cramps although I did take 1 pill late. Would this still be related to not taking the pill on time or could I be pregnant? If it is related to taking the pill late is there any way to stop it more quickly as it s affecting my relationship. Thanks.