Hi,
Welcome to ehealthforum.
Having 2 periods in the same cycle is abnormal. It could suggest possibility of pregnancy with implantation bleed, breakthrough bleeding due to birth control use, spotting due to hormonal issues etc. The emergency contraceptive taken within 72 hours of unprotected intercourse does gives you protection.
If you were already pregnant at the time of intercourse on Nov 29th and took the emergency contraceptive, then it can harm the baby due to the high hormonal dosage in them.
Visit your gynecologist for a thorough examination and tests like blood HCG levels and ultrasound scan to confirm/rule out pregnancy and look for other underlying causes that could lead to absent periods (like ovarian cyst, hormonal derangements, PCOS etc).
Visit these links to learn more on your condition:
http://www.mayoclinic.com/health/amenorrhe
a/DS00581/DSECTION=causes
http://www.nlm.nih.gov/medlineplus/ency/ar
ticle/001219.htm
Take care.