Can Emergency Contraceptives Cause Irregular Periods?

About a month ago I had sex for the first time and the condom broke, so I took Next Choice within 48 hours. About a week later I bled for about two days and I was told this was normal and the "resetting" of my cycle. Now, I am almost a week late for my period. I have never been regular, but given the situation I am getting worried. Can emergency contraceptives cause missed periods or should I assume I am pregnant