Does Next Choice Contraceptive Pill Affect Period Date?

Next choice;emergency contraceptive
Hi,
I am 16 years old, 128 pounds and 5"2". On November 23, 2012, approximately a week after my period, my boyfriend and I had sex, the condom broke, but he did not ejaculate inside of me. The next morning, about 6 hours later, I took the one-dose next choice pill. My "period" came about three days later, on the 26th of November. Despite initially getting my period on the 17th of November, it is now the 18th of December and my period is late. Does next choice change your cycle? I have been getting my usual symptoms before my period today such as cramps. I also started birth control on the 16th of December so I have only been taking it for three days. It is lo loestrin FE. I also have been taking Doryx (150 mg doxycycline) for half a year.
Thanks!