I'm 9w2d pregnant I had an ultrasound because I have been with two guys one on the twentieth and the other multiple times the first seventh tenth and the 20th of the month, and numerous times the month before. The ultrasound said 6w6d and that brought me back to the fifth of the month which makes me think it is impossible for the person i was with the one time on the 20th. How accurate was the ultrasound in determining conception?