Date confusion

Hey guys

So i have recently found out i am pregnant, and i am a little confused with how far along i am, going of my last period i would currently be 7 weeks and a few days, i went and had some blood tests last thursday and got the results, my HTP levels are only 540 so meaning the Dr said i am only 4 weeks, so cant get a dating ultrasound for another 3-4 weeks.

Any advice or feedback from anyone going through similar?

This is my third pregnancy but is completely different to my previous ones

Update

Dr got me to do a didgital pregnancy test which says I’m 5+ weeks now. It was a week ago that my blood was taken so that’s why my levels were low