I Am 55 Years Old-in Good Health And Would Work

I am 55 years old-in good health and would work out at a gym 3-4 days a week..until a few months ago. I started having difficulty breathing - first just with exertion and now most of the time. A pulmonary and heart stress test shows no abnormalities. My nose is constantly stuffy but no drainage-always dry. I often have chest pressure, but not severe. When I do light work I get light-headed and dizzy. I cannot walk up 2 flights of steps without panting. I have no cough or wheezing. This seems to be getting worse - is it asthma?