Upper right arm pain

I have had an occasional pain in my upper right arm for over a month.

The pain occurs on the outer part of the arm if I try to raise my arm above shoulder height or put it behind my back - I can't do either of these actions properly as it feels too painful sometimes even to tuck my shirt in my trousers at the back.

It also hurts sometimes when I get out of bed.

Previous injury: none
Swoolen: does not appear to be so
Sports activities I engage in: none

Possible cause: using a computer for extended periods of time with arm outstretched and/or sitting in an awkward position.

I went to my doctors for a standard checkup last week and mentioned this to him. He just mumbled something about physiotherapist and waiting list.

I have been doing some arm swinging exercises for the last couple of weeks to see if they help.

Any ideas as to what might be wrong with the arm and the best way to treat it?

Thank you.