If you had a period after the first man in August, it seems very unlikely that he would father the baby. Did you have an early ultrasound done?
Sounds like you conceived around September 20. The "7w3d" figure means seven weeks three days from the first day of your last period, which is where medical science begins the count of a woman's pregnancy time period. I know that can seem confusing because someone who hasn't been exposed to the way doctors count pregnancy out would naturally think pregnancy must begin at conception, which is not the first day of a woman's last period, when she was still bleeding and having a period and not pregnant yet at all. But the medical count of pregnancy begins there anyway, for historical reasons. It's a big obvious signal where conception is hidden and unknown, and in the old days before there were ultrasounds, they needed to have *something* to start the count. (A woman would go in to her doctor and say "I think I'm pregnant. How far along am I?" and the doctor would ask "When did your last period begin?" He would know she wasn't pregnant when still bleeding from her prior period, but it was all medical science had for a starting point of the count at that time. That's why pregnancy from conception to full-term birth takes 38 weeks, but doctors use a 40-week count for pregnancy. They're counting from a computed first day of last period.)
Anyway, around two weeks after your last period is when medical science would say you in fact conceived. Using the 7 weeks 3 days figure you got at your ultrasound, that means you conceived about 5 weeks 3 days before the day of your ultrasound, which is the 20th of September. In all cases, certainly not in August!
Congratulations on your lovely upcoming baby.