Is this normal?!?!

So I recently started birth control and about 5 days into it I had sex. We used a condom but there was a time where it fell off so as a precaution I took plan B the next morning. That was about 2 weeks ago and my period is late by 15 days. Yet for the past two weeks I’ve been getting cramps like if I was going to start my period. Is it normal to have a late period when starting birth control? Should I be worried??? I was put on Chateal if that helps.