If you're running out of air it would be good to work on spinning, try riding in the lowest gear you can stand, and pedal fast enough to get to a speed you can tolerate. If you can do that for a while (months) you will really fly when you start choosing to use higher gears.

Also if you're running out of air it doesn't hurt to see a doctor. I had a problem like that once and it turned out to be walking pneumonia. When my wife had the same problem I was wondering if she also had walking pneumonia again but it turned out to be a bunch of pulmonary embolisms.