I’m nervous my period is late 3 days!

Helpp!! I have a cycle every 24 days... I had intercourse Jan. 2/3 wee hours of the night.. I went and took a plan b not even 30 minutes later.. he withdrew.. on January 10th, I got my regular cycle on time.. normal. Well, I haven had sex since then none January. Here it is February, and my eve calendar is showing my period is 3 days late. I’m cramping like hell... could this mean plan b didn’t work and I’m pregnant? Helppp