Ok I had sex on the 29th of October and on the 3rd of November. I'm pregnant now and doctor says conception date is nov7 based on a 6.4 week ultrasound. When did I most likely conceive?

Your dates are too close to call because there is simply no way to know the exact date of conception. Ultrasound is not an exact science in terms of dating a pregnancy. It can be fairly close, may even be right on, but there is no way to know for certain. It is, however, the best tool available for dating a pregnancy early on. Unless a couple knows for certain, through the use of medical assistance to become pregnant, you can only get an approximation of a conception date.

Given that, IF you did indeed happen to conceive on, or near, Nov. 7, the sex on Nov. 3 would be the more likely source simply because odds would be greater for a larger number of healthy sperm to survive.

If this is a case of who the father might be, you will need to have a DNA test done to know for sure.

It will be most likely one of those two dates, but could be from a week earlier or even a week latter if you had sex those days.

There is no way at all to tell which date. Unless there is two different sex partners it really does not matter. If there are two or more sex partners, you will have to wait till the child is born to get a DNA test to be sure.