Does anyone have any suggestions please on how to get relief from back, neck and shoulder pain?

I am working at a keyboard for several hours a day, sometimes as many as 16, and by the end of the night I can hardly move my neck without it hurting. I end up with a deep seated pain in my shoulder blades and lower back.

I've tried different chairs, thinking that perhaps I was sitting awkwardly and that didn't help.

Any ideas would be appreciated. I really don't want to take painkillers if I can avoid that.  Thanks!