What could it be when the middle of my back hurts?

Muscle strain. Mid back pain could be caused by many things. It depends how long you had it? When you would have it? Is it all the time or just when you get up or doing somethins. When you touch one spot, can you feel the pain. Is is generalized over large area or just one spot. Is it relieved by advil or aleve (naproxen)? Most commonly is muscle strain. However, if it is lasting, need work up.