What Causes Shortness Of Breath Upon Climbing Stairs?

Hi! For three years now I have been having trouble with going up inclines (hills and stairs, walking really fast ) also when exerting myself. When I am going up inclines my legs get very tired and feel like they are starving for oxygen and I get very short of breath making it very difficult to keep going. On really bad days even my arms react as well. When I am exerting myself ( putting sheets on a bed. . . ., etc) I get short of breath. When I carry heavy things I get short of breath and my arms get really weak to the point of almost dropping what I m carrying. I have been checked by all kinds of specialist (heart, lungs, rheumatoid, neurology, etc) and all kinds of blood work. No diagnosis has been found. Do you have any thoughts?