Dont worry like I went to the midwife Friday and my stomach measured 1cm less than to weeks ago so it had shrunk! I measured 33cm and I should measure 38cm because I'm 38 weeks so I went to hospital for a scan and my baby is bigger than average and his legs are off the chart and he weighs 7.3lbs so don't worry to much go to your midwife and explain you don't feel like you have grown hope this helps
I'm nearly 6 months and am just now getting a bump that can be visible. I could where my jeans at 7 months with my last baby and she was close to 9 lbs at birth...don't worry just think the smaller u are the less stretch marks hopefully