Feeling like I'm not getting enough air.

It started two nights ago, i felt like i wasnt getting enough air, so i was trying to breath deeply and i felt like i couldnt, or that when i actually did get a deep breath in it wasnt enough. At first it was just at night and today its been on and off all day. I dont know what to do, I called my doctor and Im waiting for them to call back. Im trying to stay calm because I dont know whats going on. Im 34 wks and I've not had a problem like this before. If it even is a problem or if its my imagination..