If you take your pill consistently you should be fine. I haven't had a problem with pregnancy scares since I've been on the pill, and that's counting years of unprotected sex with my ex. Stress, over exercising, and I think poor nutrition or sleep deprivation too can all cause your period to be late a day or twoif it's much later than normal, take a test but also see your gyno. that's just my experience though, I hope that helps!