Could Delayed Periods With Abdominal Cramps Be Due To Emergency Contraceptive Pill?

I had protected sex on 28th december 2014. I also took an emergency contraceptive pill. I had my period on 1st Jan 2015 (same day as last month). I was expecting my period on 1st Feb 2015 however I am late by 7 days. I have taken 2 pregnancy tests so far and both were negative. I got stomach cramps on 6th Feb as well as today but no period. Can you please help and let me know what is going on?