Shortness of breath

Almost 30 weeks! Third pregnancy. The last 3 weeks I have been having shortness of breath. Its usually by far the worst at night. I wake up and feel like I can’t take a deep breath until I get up and walk around. Some days during the day I feel it but never as bad as it is at night. I do sleep elevated which helps a little. Last night I slept sitting up on reclined couch and that helped. I’m a nurse so I feel like I know what to look for and not so I’m just thinking it’s baby pushing against diaphragm. But has anyone else had this? I’m afraid it’s gonna keep getting worse and worse. 🥴 I do work out a lot too so I’m not terribly out of shape or anything.