August 13th? due date!!

anyone have August 13th due date? do you know exactly when you conceived? My due date is August 13th. the first day of my last period was October 28th. going off last period my due date would've been my birthday which is August 4th. but by ultrasound it is August 13th. if i ovulated later i am just wondering around the time i would have conceived i know sometime in November. :) just curious, this is my 3rd baby!!! thank you ladies