Pounding head when swimming

I am a 62 yr old nurse who has swam competively in a Masters group for > 20 yrs . I also have asthma and have done well on Advair 500 and Singulair . Rarely need rescue inhalers . 1 month ago I came down with an upper resp. infection . I had entered a major swim meet and talked myself into being well enough to swim . I wasn't . The last race I swam , before I dropped out , was 8 lenghts of freestyle and I honestly felt well enough in warm up . After the first 2 lengths my head began to pound as I swam and I had chest discomfort . I finished the race and knew I would sit out the rest . That night my coughing became much worse .
The day after I got  home I went to my MD who I have been with > 15 yrs . He said I had bronchitis and prescribed Biaxin XL for 10 days . I started to feel better after 5 days . After 7 days , I returned to swim practice . From my first length on I felt short of breath and struggled through practice . I thought each practice would get better -it didn't .Always feeling sl. SOB and much decreased exercise tolerance in the pool . Went back to MD , he said infection had made asthma worse - coughing at night , overall sl feeling of SOB - so he prescribed a 5 day blast of prednisone 50 mg OD . Went to practice last night , still struggling with my freestyle because I feel I am not getting enough air and simply not able to swim as easily or as fast as I did 6 weeks ago .
I am also Type 2 diabetic under fairly good control . Could there be a cardiac element to this sudden deterioration  in my ability to swim well . I want to enjoy swim practice again . I have also , before this started , entered another major swim meet for the end of May ,so I am  putting some pressure on myself .
I love swimming . It is the best thing I ever got involved in . Until now ,my only regrets about swim practice were that I could only make 3 of the 4 practices each week and when I look at the clock and the hour is just about up .

[National Jewish Health]

That swimming is such an important and pleasurable part of your life is wonderful.  I hope that you can continue to swim competitively for at least another 20 years, if not longer.

What you have experienced is very worrisome and definitely not what might be seen with an ordinary upper respiratory infection, acute bronchitis that should have resolved by this time, or by the sudden onset of asthma.  I suggest that you stop swimming immediately, until this problem is resolved, with certainty.

The possibilities of serious disease are real and  include pneumonia, clots to your lungs, a silent heart attack perhaps with the exception of what you describe as “chest discomfort”, possibly resulting in heart failure or a failure of your heart muscle without coronary artery disease, which is called cardiomyopathy, frequently caused by a virus and conceivably by the same virus that caused your upper respiratory infection.

The bottom line is that you are no longer the swimmer you were and that has to be acknowledged, by you and your doctor.  Your exercise capacity has been seriously and mysteriously compromised.  The cause of that compromise must be determined, without further delay and, until it is, you should not put any stress on your heart or lungs.

If your doctor is reluctant to accept the possibility of serious disease, you should without delay, seek a second opinion.

Good luck.