normally, when I have pain in the back like that is has to do with something in my neck, something pinching; or some muscle spasm in the same area, normally due to stress. Have you seen a doctor that does manipulation?
Something you can do to help at home is to do some neck stretching exercises; you can find them on the internet, just google them. Otherwise try putting your head down; your chin toward your chest and while maintaining that angle, slowly roll your head all the way around, going left then right. DO that a couple of times each direction, but don't stretch to the point of pain. Another stretch is to look to your left as far as you can and then to your right. DO this slowly and several times each direction.
Hopefully these will help.