Pain in both shoulder blades radiating down the arms, weakness. X ray normal. Reasons ?

For the past 4 years I have had pain in both shoulder blades intermittently. It is mostly in my left shoulder blade and causes pain to radiate down my arm all the way to my hand thus causing weakness. The episodes can go on for several weeks and then I can go several weeks or months with no problems. The pain also will appear briefly in my right shoulder blade and arm during these episodes but only for a few minutes at the time. I am a 35 years old and a smoker. A year ago it was so bad that I went to an orthopedic and they did a chest X-ray and also an X-ray of my spine which were both fine. He stated it was a pinched nerve and gave me anti-inflammatories to take. After a few weeks it went away and since appeared sporadically as I have stated above. I do find it odd that it is predominantly on the left side and occasionally on the right during these episodes. Any advice you could give would be greatly appreciated. I am beginning to get concerned somewhat that this keeps happening ever so often and it is the same each time.