Ramp,
When you say you had a complete physical, did that include any heart tests or tests for asthma? I wouldn't start with supplements, etc., until any and all underlying causes are ruled out. I have slightly diminished heart function and there is a difference in my ability to acclimate as compared to prior to the heart event. Lots of water, no alcohol, lighter meals, limit physical activity for a day or two and taking a few days to adjust will help. Also, especially if you have any sort of allergies, run the a/c at night to keep the air filtered. If you are on any medications these, too, may alter you ability to acclimate.