Doctor appointment #4 while pregnant

Our fourth appointment with the doctor. We are 20 weeks today. I gained 3 and 1/2 pounds since my last appointment for a total of ... not telling :) Doctor says my overall weight gain is good. They also checked my iron and I am fine there too. We started the visit off with asking for an ultrasound so we can find out the sex and the doctor said let me measure you first to see if there is a medical reason for one. Well he measured and my uterus was/is about 2 cm below where I should be at this stage. If I understand correctly, it should be at, or slightly above, my belly button, but I am still slightly below. He figured it was due to my height (I never thought I was tall by any means?) but decided to do an ultrasound just to be safe. He tried diligently to determine the baby's sex but the baby was being stubborn and didn't want to be bothered. The baby wasn't in the correct position to see the genitals, so no luck. The doctor did lots of measurements and the baby looks healthy, but is a little small. The baby is the 26% for his/her estimated size and weight. The baby is estimated to be about 11 ounces. I'll take a smaller baby for delivery, just hoping for healthy! Check out Vampy at 20 weeks. Can you believe we are half way through. It's amazing how time is flying.