Confused about how far along I am...

Hello all! I had my first prenatal appointment today to confirm pregnancy. I thought I was almost 6 weeks along but the doctor said I can only be 3-4 weeks, which makes me really confused! I had a miscarriage last month and when my HCG levels got down to 0 on March 27, we got the ok to try again and I believe that is our conception date as well. Since I don't have a LMP due to the miscarriage that I can calculate with, I assumed calculating from my possible conception date would put me at 5 weeks and 6 days and that's what so many calculators online tell me as well, but the doctor is saying otherwise. Does the miscarriage affect the calculation?