so my baby is measuring a week behind than what we originally thought

Janice
My baby is measuring a week behind what we originally thought. Can he just be small? Has anyone had this? I'm confused because I felt pregnant early on and I took a pregnancy test 3 days before my missed period (my cycles only 28 days) and got my positive. I've had two ultrasounds and another next week. Heartbeat was great and we seen our little bean moving. I'm 10 weeks pregnant according to his size.
The reason I'm confused is because I don't feel a week behind is accurate. That's why I wanted to know if anyone else had this happen.