I have pain under my breast and I can tell it's nerve pain. It goes around to my back and it's VERY painful when it occurs, which is usually when I'm twisting or trying to hold the phone by cradling it on my shoulder. I can tell it's hitting a nerve in just the right way (or wrong way, I guess). I had my surgery more than 5 years ago. If you can identify what kind of pain it is (e.g., stabbing, gnawing, pins and needles, pounding, etc.), then you can determine if it's a muscle or a nerve pain. Hope that helps.
Hugs & prayers,