How can u hav sex nov. 6 get period next week a day late n say u pregnant the following week but doctor say due date sep. 10? is that possible?

Dating off?: With a september 10, 2014 due date the date of conception would be december 18. This would mean a positive pregnancy test around now. This does not work for positive pregnancy test in november. Do you mean due date august 10? That would give a date of conception of around november 17, and a positive pregnancy test early december. Some women bleed with implantation and think it's a period.