When did I conceive? Sex on may 23-26. Period on june 5th. Sex again on june 13-15. Ultrasound at 11 weeks says my due date is march 8th.

If... If you are sure of your last menstrual period that is supposed to be a more reliable indicator of the due date compared with your ultrasound estimation. If that is the case then the conception date is around the days you had sex in May. If you are not sure of your period and the US is giving precise dates( it usually varies few days) then conception happened in June.