It sounds like you conceived on or around the 15th of October. At 6 weeks 6 days, the margin for error would be pretty small, maybe +/- a day. You can't use an ultrasound to replace the need for a DNA test if sex with two guys was very close together, but getting an ultrasound this early is very helpful.
They based it of the measurements
They didn't give an ultrasound when you first went in, but then you did have an ultrasound on November 18 and were told by them that you were 6 weeks 6 days, from the measurements of the embryo?
Yes the first time I went in to confirm I was pregnant. But they didn't give an ultrasound. They just wanted to check..
You can give a pretty good guess. You say the last time you had an ultrasound, you were told you were 6 weeks 6 days? Does that mean you had an earlier one also?