What Causes "pins And Needles" Sensation In The Back?

My question is this...I have this feeling between my shoulder blades that feels like i have pins in my shirt. I know that this sounds strange, but it will feel like out of nowhere i get a couple of needles stuck in my back. I rub the spot, itch it, put pressure on it and nothing happens. If i leave the feeling alone for 10-15 seconds it goes away like someone pulled the needles out of my back. What is this?!