Hi,
I just started this month using mononessa. I was on loestrin 24fe for two years prior. A few days after I started using the new birth control I had unprotected sex. I thought it was okay since I never skipped a pill before. I was supposed to start my period on Sunday and now it is Tuesday. Is it possible that the new birth control wasn't working yet and I'm pregnant? I'm very worried!

It could be that the pill has just upset your hormonal balance. You might not be pregnant but have a late period because of the new medication. It is a good idea to ask your doctor about it either now or after you have waited a few weeks and have seen no period.