I too had sob for 1 and a half yrs...lungs are clear....oddly enough my cause was found because of severe spine pain which was separate from the shortness of breath.....I had an E M G muscle test done that showed abnormal findings....my muscles are weak in my diaphragm and I was diagnosed with a very, very rare disease called "Stiff Person Syndrome" that effects the brain and spinal cord/central nervous system....had I not gotten that E M G, I would have never gotten an answer.....many muscle diseases can effect breathing.....I suggest you get an E M G (muscle test) done to find your answer....everything else has been normal or very close to normal....there is ALWAYS a cause for shortness of breath !