What Causes A Delayed Period Despite Being On Birth Control Pills?

Hi, Im a 30 year old female who just lost my virginity 5 months ago. I am on the birth control pill and have used condoms when having sex, the man I've been with has also had a vasectomy. I did get my period after the last time I was with him over a month ago. Normally after my last sugar pill I would get my period, however I just started a fresh package of pills and I still haven't gotten my period. I also took 2 home pregnancy tests both came out negative. What should I do?