Why does my back hurt like this?

Every once in awhile, it feels like all the muscles in my back, down to somewhere around the bottom of my rib cage, are tensing and won’t let go. When I move, it feels like I’m stretching muscles that I slept on funny, but it always happens midday. I haven’t done any strenuous lifting or exercise, I have pretty good posture from being a dancer for a long time, and I have no muscle-related medical problems. I don’t think it’s breast related because my lower back isn’t effected. Ideas?

Also, does anyone have any remedies that will ease pain that does not involve medication? Any stretches, etc that might help?