This could possibly be costochondritis. Many with fibro have this too. I will get attacks of this. There is a link in Fibro 101 all about it so you might want to read that and see what you think.
Fibromyalgia can affect muscles, tendons, and ligaments most anywhere in the body. about the only thing on me that hasn't hurt at some time or another are my ear lobes! No muscles there!
Sherrine