Prop up a pill along your spine and have extra for your head!!! It helps me sit and sleep... I have asthma bad and it helps me. my asthma is even worse since i've been pregnant and doing that helps me sleep and sit!!! :) hope it works for you
It's likely from the way baby is sitting and your position. The only thing you can really do is be creative with your pillows. I sleep on my side with a body pillow tucked under my belly and in between my legs, a small pillow under my ankles (on days when my feet get swollen) and one beside my back to keep me propped up in case I roll to my back. I can't breathe properly when I'm flat on my back.
Are you laying on your back? If so try not to it makes it harder to breath because baby pushes on your lungs