First dr. appt. for this pregnancy today!!

I had my first doctor appointment today, and I guess it went okay. I left there a little confused, but here is the story. After the usual b/p check, weight, etc. She gave me my est. due date based off my last period to be: March 27, 2007. So once I get in the room, they do a transvag. u/s. At first he sees the larger sac to the right and thinks that is it. Then he scans over to the left and sees the much smaller one. So he studies this for quite a while, and tells me that he is 99% certain that the two sacs do NOT mean twins! He's still confused though as why I have two at such different sizes. He said the bigger one could be blood left over from implantation, and the smaller sac is actually where the baby will be, and I'm just not as far along as he'd thought. He said I could have ovulated much later than normal, which would have me still in the very early stages. He asked me if I have had any spotting yet, and I said no. So he told me that if I was to have ANY to call him at once. He sent me for more bloodwork to check my HCG levels, and I will hopefully get that back tomorrow @ lunchtime. I go back for another u/s next Tuesday -Aug. 8th. Here is the picture from the u/s today - the smaller sac on the left is what he's thinking is the actual pregnancy. If so, I'm guessing now that my due date is April 3rd. I'll know more both after tomorrow and next week combined. All I know is from stressing so bad during the appt., my stomach paid dearly after it was all over! I'll keep everyone posted as I find more news out.