What Causes Delay In Menstruation Other Than Pregnancy?

Hi, I had unprotected sex on the 3rd of Jan , I took ellaone on the 6th of Jan & had a withdrawal bleed on the 8th. I assumed I would of had my next period around the 5th of Feb , I still haven't had my period. I've took 2 pregnancy tests & they were both negative. Is there a chance I could be pregnant?