Today's appointment

So I went in today and the doctor's test came out positive.  They decided to do more bloodwork and I'll be going back in on Thursday for the results and more info (including prenatal vitamins, next appointment and all that).  They gave me an estimated due date of September 2, 2010 which magically jumps me from the 4 weeks and 3 days I'm pretty sure I am to 5 weeks and 4 days.  I told him that I know it's going to be later since I've been keeping track of my cycles and all but he said that he's just going to wait until they can do an ultrasound and measure to be exact.