Can't breath

I swear I'm going to need an O2 tank at any point. I can never seem to catch my breath, I'm constantly struggling for air. I'm only 32 weeks. I have an ultrasound Monday to see how big baby boy is and I have a feeling he is pretty big. I don't have any health issues thank the lord. But I don't know how much longer I can go on like this. I hope my Dr can come out with some kind of solution. I'm a nurse so I know all the tricks to help facilitate better breathing and nothing is helping!!

I know I can't be the only one????