I have the same problem with the breathing. If your dr's can't find out what's wrong ask them to check for Pulmonary Hypertension. Alot of times it gets overlooked and labeled as Asthma. Are you fatigued alot? Adema also is related to this. Just a thought.
I have had the same problem over the years and it comes and goes. It feels like you can't get a good breath. Yawning seems to help me too. I don't know what the cause of this is, but I can tell you that I had the problem when I was playing sports in college...continuing through college...and now when I am nearly 40. It does not seem to have anything to do with physical fitness because I have had the problem in my "most fit" periods of life. I thought I was the only one with this problem; I guess this may not be unusual.
As I understand your message, you are having difficulty breathing. The main causes of that come from lung disease, most commonly asthma in children and young adults, or heart disease. Perhaps the most common cause is being in poor physical condition, for lack of exercise. And one other common cause would be a chronically “stuffy” nose. Yawning is seldom a symptom of lung or heart disease. It is most often seen when a person is experiencing anxiety, for any reason, or when a person becomes concerned, even obsessed with his/her breathing, whatever the original cause of shortness of breath.
My best advice is that you see your doctor to have your lungs and heart checked-out. If they are OK, you should get started with a program of regular exercise, starting with walking and building-up the exercise from there.