this should go to Dr. Hansfield or a medical doctor on the site.
when they calculate your pregancy date they count back to your last period as that is the most accurate way, you actually ovulated/conceived anywhere from 9-14 days ago,so no you didnt get pregnant on BC, it's just the way dr's accurately date pregnancies
You have been pg for about 2 weeks. They add 2 weeks to that, and it makes 40 weeks total for pregnancy (10 lunar months). It calculates your due date by the FIRST day of your last period...because MOST women do not know the day they got pg, but can usually come up with the first day of their last period.