What Cause Muscle Spasms In Neck And Shoulder?

I have been experiencing muscle spasms in my neck and left shoulder for a couple years now and my Dr doesn t seem to know what might be causing it. Instead he just treats the symptoms will muscle relaxers and pain pills, Which I don t like taking. I would rather find out whats causing it and cure it then just treat it. And for about 8 months now my back right across where my bra is constantly itches. It never stops. What could be causing this & how can I stop it