What Causes Delayed Period After Taking Emergency Contraceptive Pill Followed By Sex?

My menstrual cycle is 28days, my last period began on August 2, I had sex on August 14, the condom burst, I then had emergency contraceptive pill on August 16. My period was due on Monday August 30, but it still hasn't come. I had a negative home pregnancy test yesterday, should I now discount pregnancy? or should I try another pregnancy test in a few more days?