Can Having Unprotected Sex While Skipping The Pills Cause Pregnancy?

Hi Docter, I have been taking birth control for a few years, but in the last few months I misses some pills. Last month I miss 3 pills, on day 16, 17, and 18, out of 28 days. I didn't double up on pills after that, and i had sex on those days and the days before, and after. Now my period is 11 days late. This is not normal for me. I have never been more then 1 or 2 days late. Could I be pregnant? And what should I do next?