Leah, I had the same thing at 28-29w pregnant (can't remember exactly when) - I was 5cm too small. I had a scan and guess what? The baby is fine. In fact, I am now freaking out about the huge head circumferance the baby had back then.

I was then told off a couple of weeks after that by another midwife for having a small bump. Stupid woman.

I was asked today when I'm due - when I said "last week" I don't think the poor woman asking believed me, the bump is still on the small side. But my baby is big and healthy, so I have given up caring what others say.

Just be happy - a smaller bump means less weight to lose later and you'll be back in normal clothes sooner.