6 weeks and 4 days no heart beat or fetal pole

Hi.....I'm really confused right now.  I had a vaginal USD done exactly 7 days ago with my regular GYN.  They only saw a gestational sac and dated me at 5 weeks.  I took another vaginal USD yesterday with my OB and the gestational sac grew, but they saw no heart beat and no fetal pole.  They also said they think they may see a yolk sac, but they weren't sure (It was small).  At that time they told me I'm probably 5 weeks.  My OB said to come back in 2 weeks to do another USD to see if they see anything.  If they see nothing then it's a miscarriage.  I go to see my regular GYN next week for a USD. Should I see something already?  I'm seeing two DR's.  I don't understand how I can be dated 5 weeks two weeks in a row.  I've had no bleeding, slight pain in my left side since last night, but that's it.  I don't have too many pregnancy symptoms anymore.  Limited breast tenderness, I don't really feel sick.  I just don't feel hungry.  My LMP was July 3 and it is now Aug. 18.  My pregnancy test came back positive 3 days before my missed period so I don't see how my dates are wrong....Help please....This would be my third child...no history of miscarriage.