Hi, I Am Having Some Trouble With My Upper Left

Hi,
I am having some trouble with my upper left back. I don't know if it is just a knot, or if there is a tear, or something in the muscles. It feels like a knot that rolls when pressure is applied, but it also affects nerves somehow. When I hit certain spots (in the knotted area, which is under the shoulder blade, or at various locations up and down my left arm) it causes any, or any combo of the following: deep ache in my left arm, worse on the lower half, and tingling or numbness in my fingertips and hands. It is worse when I am not active and especially bad when sitting at work. It also kicks in when I cross my legs. I am not sure what sort of treatment plan I should pursue. I have been using heating pads, icing it, and taking naproxen.