My doctor says I have a healthy heart and lungs. I don't smoke, drink or do drugs. Why do I get tired so fast out of breath always have palpatations?

Shortness of breath. Although heart and lung issues are the predominate reasons for shortness of breath and palpitations, there are other less common reasons for your symptoms. It's possible your thyroid is over active causing some of these symptoms. See your doctor again to see if your thyroid is over functioning.