18 weeks pregnant i feel fat and uncomfortable?

It definitely could be because you're so small. This baby is getting bigger and bigger and especially when you're of a smaller build all that pressure can be seriously uncomfortable. I understand perfectly. I'm 5'8 and my son loves to lie really really low in my pelvis so while I am a lot bigger than you, it is really uncomfortable. I get quite out of breath and tire very very easily when I walk around so I understand exactly where you're coming from. However I think it's just how it's going to be. When baby gets bigger everything else is compressed and you get uncomfortable and it's just really exhausting. I think we're just going to have to deal with it though Im afraid.

I'm sorry I cant give any real advice but I seriously understand where you're coming from. I'm 25 weeks along and it just gets harder from here so I honestly wish you luck :). This is my first pregnancy and it sounds like yours too so I understand completely what it's like with all these new feelings and sensations and not being sure what is what and whether everything is normal. Pregnancy is lovely but it can be a total pain sometimes!

Good luck though!