im not sure what it is honestly, but i have a very similliar problem... my chest and ribs feel like someone is pushing on them and beating them and my upper back and rear rib area hurts too.... but the pains in the side of my breast dont hurt near as bad and have yet to hurt when my back and chest do...
i feel the onset to the pain as somekind of a pressure,disconfot deal, and i know the pain is going to start within a few minutes and i start trying to stretch it out.... for some reason it seems to temporarily help...
but with mine, it comes and goes... every few days... sometimes a few times a day... never know... but it gets to the point that i cant pick up my son and he weighs under 8 lbs!!
sometimes it hurts so bad that i (for lack of a less harsh word) i vomit..... but afterwards, it feels better... i dont understand it, but i am curious to know if any of this sounds familliar to you