Is your OB concerned about your or the baby size? If not don't worry about it. I'm 37 weeks and ppl still can't tell if I'm pregnant when I wear a light sweater or from the back.
The pressure your feeling in your pelvic is your body preparing for that big day, so it's normal. I had the same pressure at start of 3rd tri with the clicking & popping of my hip/back bone. Buy a belly sling to help ease the pain and hold some weight of your belly. Though it maybe small your body isn't use to carrying that much weight in ten one area. Go to Babies R'Us to buy one. Good luck & congrats.
I'm 34 w an measuring over but the pain is prob your pelvic bones shifting preparing your body for the big day