My Ex Is Pregnant And Either Her New Boyfriend Or

My ex is pregnant and either her new boyfriend or I is the father. She went to the Er on Aug 17 for kidney stones. They did blood work and it came back - for being pregnant. Her last period was around Aug 7-8ish. On sept 16 she showed + on a home test then went to the hospital and had a vaginal ultra sound done and they said she was approximately 6 weeks 5 days. She went the next day to her Dr. for blood work where they told her she was 30 days. Which one is more accurate? what do you think the possible conception date was?