Your egg can only be fertilized when you ovulate--when there's an egg available. Ovulation generally occurs 11-16 days before the start of your period, and you're most fertil in the 2-3 days preceding that, with fertility possible extending from 5-6 days before ovulation until 12-36 hours afterwards--so anywhere from 9-22 days before your period, depending on when you ovulate. Getting pregnant 8 days before your period is not likely at all. IF you're pregnant (and since you had your period at all, your chances are still slim), it would have to have happened before the incident on March 13. But since you had a period and your test was negative, I'd be willing to bet that you're not pregnant.
at 11:27 AM on Apr. 18, 2011