That's the gas they pump into you to give them room to work. Now that you have it, it's going to hurt for a while. Mine was also in the shoulder and it hurt like hell for about a week off and on and pinged on me for another week after that. As much as it hurts, if you work that part of your shoulder you can start to break up the gas. Worst part of recovery.

That gas pain is real. Goes straight to the shoulder after parking itself under your diaphragm. They gave me the strong stuff for that one. Moving around helped me.