Measuring small

Just wanted to hear if anyone has experienced anything similar. Everyone is saying I look so small and I was so upset when I measured 26 weeks at my 29 week appointment. First baby and doctor said if I continued to be small i would have an ultrasound to check he was growing well. At 31 week appointment I was still small measuring 28 weeks. We had an ultrasound for fun at 30 weeks and baby looked pretty chunky but it does worry me a little. Including his 30 week picture just for fun.