Please also remember that if a doctor says "You're 8 weeks pregnant," he or she means 6 weeks from presumed conception. In other words, the doctor always begins the count on the first day of the last period, not on the day he or she thinks you might have conceived.
If you didn't have any more sex with Mr. February after the period, the father would be your March partner. Get an ultrasound on what would be your 6th or 7th week (counted from the first day of your last period), and ask them for your estimated due date. Then either use an online conception calculator or else just count back 266 days from the estimated due date on a calendar, and that would be your probable conception date.