Babe, tell me to shut up if you want,i hope I'm not being insensitive but just putting it out there...is it possible that maybe you m/c the first pregnancy, and concieved again without knowing? It's a bit of a long shot but maybe that's why the dates are so weird (only possibility I can think of really, seeing as you were sure?)

I just hope that scan shows a healthy, squirming little bubba for you, SO much :hug)
This happened to me with my 4th m/c. I actually thought I was still experiencing m/c symptoms from an earlier loss in Dec 08, however my HCG levels were around 3,000ish which is consistent with a pg @ approx. 5 week - OBS thought this was another pg & loss given those levels - this pg/loss was in Feb 09.

I also was 'behind' my dates for my DD. I thought I was about 9 weeks, but I was dated back to 7.5 weeks - seemed I O late....