Are you still measuring at 31cm's. I know when my MW used to check my tummy they usually give 2cm's either way as a sign as 'normal' but tbh another MW at my antinatal classes said its a load of rubbish as women and their tummy's are all different and all measure differently anyway and it depends which way baby is laying at the time.
If your worried yourself mention it to your MW hun
Anyway - I hope your ok and getting a bit of rest now