What Causes Stiffness And Tenderness In Lower Thoracic Area?

I've had stiffness in my lower thoracic area for about 3 months. It has now elevated to tenderness in a localized T area..not sure which number right below my bra strap. It hurts but nor debilitating and nsaids will not relieve the pain. it doesn't hurt when in bend..only when I arch forward or backward and it is increasing.