pain behind the right shoulder and the right arm

I have had this pain for the last five days…its a dull nagging pain which I think originates from the upper back behind my shoulder and goes down the entire length of my roght arm. A pin killer helps but once the effect wears off, the pain is right back. What could be the reason and what should I do alleviate it? Any helpful exercises? Who do I see….a GP? An orthopaedist? Please help.