Measuring Further Along?

I am 9w5d today with baby#3 and at my 9w1w appointment ultrasound it confirmed 1 baby and measured exactly 9w1d but she said my uterus was just under my belly button! I was shocked because I thought it was still down in the pelvis. She said it gets bigger faster with each pregnancy. Then when I saw the midwife she felt my stomach and her eyes bugged out and she said How far along are You? I said 9 weeks she grabbed the tape measure and said I measured at 12 weeks and asked if I was sure there was only 1 baby. I said that's what your ultrasound lady said. She felt again and just seemed puzzled. I asked if I should be worried and she said No.....anyone else have a similar experience or any words to make me feel Better? I felt like I couldn't hold the pooch in very much anymore....Now I guess I know why. Should I be worried?