Don't get discouraged!!!
You are clearly doing incredibly well to have lost the weight.
Using swimming was brilliant so as not to suffer an injury from running.
The only trouble with swimming is that in the water you are weightless.
So as was mentioned above unless you are swimming really hard and getting your heart rate up, there will be little transference to tennis or running fitness.
It must be frustrating not to have even made even greater strides.
Just be patient - so you may not win the Australian Open - shoot for June and the French for your first title
The advice above of using a stair climber - or cross country skier or even stationary cycling and doing HIIT workouts is what will eventually get you the kind of "wind" you are seeking for tennis.
HIIT - High Intensity Interval Training http://www.intervaltraining.net/hiit.html
For those who are suckers for high tec gizmos (like me) you may get a kick out of using a heart weight monitor when you work out - even give it a try when you play tennis.
Obviously this is not essential, but getting your heart rate into a higher zone may be a goal that will give you a yardstick to how hard you are working out.
You may even be quite pleasantly surprised to see your heart rate is indeed high - and as the weight comes off you can be expecting to see the results on court you desire.
[I use the Garmin Forerunner 205, although Timex and Polar are probably the two most popular brands, and Garmin makes a waterproof model for swimmers.]
Finally, are you sure you do not have the fairly common problem of "exercise induced asthma"?
I remember someone earlier this year started a thread that they got short of breath on court, and a couple of weeks later gave a follow up that they had been diagnosed with exercise induced asthma.
From the Mayo Clinic website:
If you cough, wheeze or feel out of breath during or after exercise, it may be more than exertion causing your symptoms. You might have exercise-induced asthma. As with asthma triggered by other things, exercise-induced asthma symptoms occur when your airways tighten and produce extra mucus.
If you have exercise-induced asthma — also called exercise-induced bronchospasm (BRONG-ko-spaz-um) — physical exertion may be the only thing that triggers your symptoms. Or, exercise may be just one of several things that trigger your asthma. But having exercise-induced asthma doesn't mean you shouldn't exercise. Proper treatment of exercise-induced asthma and precautions can keep you active — whether you're strolling through the park or running a race.
Exercise-induced asthma symptoms may start a few minutes after you begin exercising, and they may continue to worsen for another 10 minutes or so after you've finished a workout. It's possible to have symptoms both during and after exercise.
Feeling a little short of breath or fatigued when you work out is normal, especially if you aren't in great shape. But with exercise-induced asthma, these symptoms can be more severe."