I have just had an x ray done due to the same pain! Glad to have stumbled upon this topic wot a relief!
I jus spent the last week with the dreaded thoughts something was terribly wrong, that dull ache sorta top leftside of my chest, and i couldnt quite tell at the time if it was muscular or inside my chest just knew it didnt feel right , it has since gone away again but im still waiting for my results, i suffer alot with shortness of breath (anxiety related apparently) so im helping it will put my mind at ease as well.