Late Period, but negative test last week

Need advice! I’ve been taking birth control pills starting March 22nd during the middle of my cycle. I ended my last pill on April 11th. Took a pregnancy test on April 13th to be sure I wasn’t pregnant and it was a negative. I’m now 3-4 days late for my period. I also did take an emergency pill on the 15th since my husband and I did have unprotected sex at that time. Why is it that I haven’t received my period still?? I’m stressing out as we do not want to be pregnant due to circumstances.

Thanks in advance!