I was just prescribed birth control pills for the first time and started taking Levonorgestrel-Ethinyl Estradiol. The doctor advised that I start them on the day of my period but I took the pill on the day I believed I was scheduled to start my period. But to my surprise my period has still not started and is now considered 4 nearing 5 days late. I do know BC can cause you to skip periods but I find it hard to believe it could take effect that quickly. I have not been sexually active in months and have had regular periods since then so I do know I am not pregnant. Thanks.