Im scared im pregnant....when can i tell?

My bf and i had last night. im on birth control and we used a condom but for some reason i get very dry and the condom popped right when he d. i felt it trickle down my backside so i know it got on me. is there a good chance i could be pregnant? and when is an accurate time for a test? does birth control affect pregnancy tests? my period should be coming by the end of this week according to my pills. i dont want to get a doctors opinion yet because that involves telling my mother more than she needs to know right now. please help because i would like to know as soon as possible:)