I don't have Fibromyalgia, but like Grizabella, I had Tietze's Syndrome some years back. As she rightly said it's an inflamation of the connective tissue between the ribs, and it's proper name is Costochondritis.

It's an extremely unpleasant condition which involves the front of the chest or the shoulders, or both. It can be quite painful, and is often mistaken for heart diseases like angina.

Costochondritis usually, but not always, involves one side of the breastbone. Sometimes the pain can extend to the shoulder or arm on the involved side. When costochondritis is accompanied by swelling of the areas surrounding the cartilage, the condition is called Tietze syndrome. .........

http://www.emedicinehealth.com/costo...article_em.htm

When I presented with this pain, I went through just about every heart test available, but naturally they were all normal. Eventually it went away by itself without any treatment at all.

This may not be what you have peekaboo, but it's something worth considering.