Hi there. Females can become pregnant at any time during their menstrual cycle, however the peak of fertility happens just a few days during the menstrual cycle—usually two days prior to and two days after the ovulation date (when they release an egg). A female's egg is normally able to be fertilised for up to 48 hours after it has been released from the ovary, while sperm can survive inside the uterus 48–72 hours on average.

If you had your period on 16th November this would indicate that you were not pregnant at this time. If you had sexual intercourse on 24th November and now you are pregnant (I'm assuming you did not get another period) then I'd assume that you conceived around 24th November.

When you see you general practitioner (GP) for confirmation of your pregnancy they will be to calculate when you were likely to have conceived, and they will also be able to work out your due date. Take care.