There is no way to know the exact date. Sperm can live in the fallopian tube for 5 days so the date of conception isn't exactly the day you had sex. Most go by the date of your last period estimating 9 months and they usually add a week or two to that.
Sometime in November depending on your last period.. How many days are your cycles. 28 days or more. We are planning for a september baby so I would have to get pregnant in December. Still waiting to find out but it would then be a September baby. If your due in Aug then you would have to have gotten pregnant in November. If you are a 28 day cycle then from the first day of your last period count to 14 and you may have gotten pregnant sometime in there.