Hi, For The Last Month Or So I Have Been

Hi, For the last month or so I have been experiencing sharp intense discomfort on the left side just beneath my breast and radiates to my back. I do not believe it to be cardiac in nature as I have found that the symptoms can be positional. Worst positions are of course lying down, leaning to the left while in a chair and sometimes even just standing. Other than the intense pain, at times it takes my breath away. Is it possible that I could have a non-traumatic rib fracture, or simply pulled muscle? Seems very odd to me. I am a nurse so lots of repetitive movement but I take body mechanics very seriously. I am also a runner. No significant PMH. Any suggestions???