What Causes Delayed Periods While On Contraceptives?

Hello, I am worried that I might be Pregnant. I have anziety so I am serious worrying. I am on birthcontrol and suppose to get my period. I stopped taking them sunday. I am sexually active (only since christmas) I do not have my period yet but I am sometime irregular and I am just worrying. Me and my boy friend kind of use the pull out method (i know we are stupid and should always use a condom, its that stupid heat of the moment thing) but we have sex then put on the condom then continue and he ejaculates. Someone please help me.