Mine does be the same im 21 weeks some days I look pregnant and others I just look a little bit bloated.. I think it's due to fluid retention and just bloating or where babies lying :)
Yes its normal its depends on your fluid intake. If you notice in the morning your small once you get up and move around and drink fluids it gets back to your normal size. Do drink alot of water tho, its for the baby when you drink water you are creating more amiotic fluid which helps cushion the baby and gives him/her more room to move around.