If my estimated conception date is december 6 based on early sonogram what is the likelihood of it being from sex on november 29th unlikely right?

Depends: Ultrasound performed at 7-10 weeks is supposedly accurate to within 3 days. The later the ultrasound, the less accurate it is. If ultrasound done at 15 weeks, it can be more than a week off in determining gestational age. If you had a transvaginal ultrasound at 7-10 weeks and it gave you a conception date of dec. 6, you very likely conceived between dec. 3 and dec. 9. At 15 weeks, nov. 29-dec 14.