Uterus sizing for gestation

So, I went in for a very early ultrasound, as I was having some abdominal pain. It was explained, and everything is okay. However, the doctor said my uterus measured at 7 weeks. Since my last period was 4/06, there is no way I could be 7 weeks. I’m at 4 weeks 4 days.... Could this mean twins? Im so early the baby wasn’t visible... so confused! And I can’t find anything online about it!

Also, I tested very early positive, over a week before my expected period. I am extremely naseaus all day, unlike my previous pregnancy as well.