Whats wrong with my shoulder/back muscle?

Okay, So for the past year, Ive been having awful pain in my upper left muscle right above my shoulder blade but not technically on my shoulder, right underneath. I'm not sure whats wrong with it, Should i see a doctor? Or is it just a strained muscle? It occurs when i work out, sit in a chair, or at a computer desk. It feels like its constantly tightening and tensing up and then it releases and feels like a coolness released. Please help asap?