I have the same problem, just as you all have described. It comes and goes, inflaming tissue. In the research I've done there are no real results although many women have done extensive tests. It feels like a pulled muscle, but it started with a spasm that was so violent (out of the blue) that it put me on my bed gasping for air and feeling a pain indescribable. Ever since, it's been a place that gets irritated, swollen soft tissue-like. Some blame underwire bras and the reconfiguring of the fatty tissue due to them. This also feels like a muscle separation from a rib. It's bothersome. Advil doesn't work. Neither does stretching. Almost scared to put ice or heat on it for fear of irritating it more. It usually goes away after a few days, but comes back, especially if I exercise or stretch lightly. HELP??