What Causes Pain In Neck Radiating To Shoulders?

Hi, i am male 36 year old, and i am suffering from pain which goes from my left side of the neck to shoulder and then to arm and hand....

In the beginning of this problem i went to see number of doctors got Xrays but nothing worked and the bone structure is fine as the doctor said...

now the pain increasing...

i feel that the problem is either in my muscles or nerves...

please help...