Hi!
If you were my patient, I would advise you that we would need an ultrasound to help us determine how far along you are. Plan B will interfere with the normal cycle by delaying ovulation. IF you are already pregnant, Plan B will NOT cause a miscarriage, nor has it been shown to cause any harmful effects to the developing baby. An ultrasound done in the first trimester is accurate within 5-7 days so should give you the answer to your question.
Good luck!
Dr B
The first day of My period before the my last on the 27 was on December 13. So I shouldn't have been ovulating on December 21st right?