Confusing edd

Sorry this is going to be a long post but any feedback negative or positive would be appreciated. I found out I was expecting much to my surprise on 7/28/20. pregnancy test was a faint line but very definitely positive. I waited a couple weeks to call doctor but after speaking with them they wanted some blood work and to do an early scan because I was still breastfeeding my 12 month old. Went in at what I thought was around 5 1/2 weeks or so and HCG a little over 3,000. Went in for ultra sound on 8/20 (somewhere around 6 1/2 -7 weeks) and only thing found was gestational sac and yolk sac. Obviously, I assumed the worst at this point because if I got a positive pregnancy test end of July there is no way I could be that early almost a month after. I go back a week later to confirm loss (8/26) and HCG 35,000 and now doctor sees both sacks and the baby with cardiac movement of 106 but measuring 5 weeks 6 days. She was very optimistic and told me that if she didn’t know when my positive test was, she would have just assumed everything was actually how it should be. So somehow I test positive for pregnancy on 7/28 but am only five weeks 6 days on 8/26? I’m just really confused on how I can be measuring that far behind without something being terribly wrong. The doctor had no explanation but said strange things happen sometimes. Can anyone share stories with me. Good or bad. Obviously what will be will be and I so want to be excited and enjoy this if possible. I just wanted to read others experiences with this if there are any.