November 29 would be the suggested conception date for an August 22 due date.
So I'm looking at November 29 (which comes from your estimated due date), and looking at your ultrasound on January 9 saying 7 weeks " +/- 6 days." If it was at the "plus 6 days" that would take conception back to November 29.
Do you know anything about why your doctor said +/- 6 days? That is an unusually large margin for error for a seventh-week ultrasound. Usually so early in pregnancy the margin for error is only given as +/- 1 day or 2 days.
In any case, it's hard to think of any factors that would suggest the first guy is the dad, with the only possible exception that you have relatively short menstrual months. (I.e., if they are 24 days, you would ovulate around day 10, and if they are 26 days, you would ovulate around day 12.)
If we were to create an example using the shortest scenario to test the situation, you would ovulate at 10 days, which would have been November 28, and sperm from November 22 would need to be still viable after 6 days in your reproductive tract. This long of a lifespan for sperm is said by some (but not all) research to be possible, but other research suggests that by the time sperm is six days old, it is not strong enough to penetrate the egg anyway.
This means the parts of the situation that do not favor the first guy are that the farthest out scenario involving a 24-day menstrual month still does not quite point to him, and you don't always have 24-day menstrual months anyway, sometimes they are 26 days. And, sperm isn't too mighty by then if it is even still alive. And, your doctor did an ultrasound and saw and measured the actual embryo, and told you that your due date is August 22, which points to getting pregnant on November 29. And, you had sex on November 28 with lots of new sperm that would penetrate the egg with ease.
I'd say, probably the ultrasound that said your conception date was November 29 was correct, and if your conception date was November 29, that points pretty much only to guy #2. In your shoes, I'd go through the pregnancy pretty certain he was the dad, and would get DNA tests done with both guys once the baby was born just so you will never wonder, and then forget it forever.