I was put on Previfem in 2009 and switched to Estarylla in 2014 without any problems. I've always been able to predict my period to nearly the hour every single month. 3 months ago I switched to Ortho-Cyclen and my period was 2 days late the first 2 months and a day late this month. Plus my PMS has never been worse than what I've experienced for the past 3 months. It doesn't make sense to me since it's suppised to be the same medicine. Does this ever happen to anyone else?