Very normal unfortunately. Our hearts are pumping tons more than usual, baby is taking up room & pushing our organs out of the way & our bodies are going through a lot of changes. Try laying on your side & drinking tons of water. Do not be laying on your back. This is very hard on your body & limits breathing even further. When we xant breathe neither can baby.
Im having this and I hate it!! Just sitting down makes me feel like I can't breath. This was what I hated in my last pregnancy and was dreading it this preg also. I feel like im dying a slow horrible death haha it doesn't get much better im afraid untill the end when you drop :)
It's normal, baby pushes all your organs up and then sometimes even can lay on your lungs. Try to elevate your head. It'll go away when you get far enough along for baby to drop.