Unfortunately, you're really NOT going to know if you're late because BC may have thrown your cycle completely out of whack. Are you still having unprotected sex? If so, then it's going to be even harder to pinpoint. If you are NOT having unprotected sex anymore, then you can take a test two weeks after the last time you did. That should give you a pretty reliable answer as to whether or not you got pregnant.
I assume you're not trying to get pregnant since you were using BC? I hope things turn out the way you want them to!