Early us at 7 weeks. duedate 7/28 ob told said count bk 5 weeks for conception date. 11/4 which is exact day of sex want r chances it's wrong?

Ob doc is correct...: It is correct to count back 2 weeks less than the number of weeks pregnant (that's why the 5 weeks) to find the conception date, because that's just how doctor's count pregnancy weeks. The exact day of sex is the actual day that the woman had sex, on or within a week on either side of the the estimated "conception date". There is no more exactness to the dating, because all dates are estimates.