Random Breast/chest pain for a few weeks

I am having random breast pain for a few weeks now. I get pinching pain for a moment on left side of chest which eventually fades away but it keeps coming back. Sometimes everyday and sometimes once or twice a week. Assuming it could be a heart related problem I got it checked but everything was clear then as this pain occurs in both chest side and upper back I got an x ray done two months ago but everything came out fine and doctor suggested it might be a posture issue As the pain started reoccurring now, I am not sure what is causing it It is not cyclic as I'm having the pain everyday The pain is mostly on the left side I do not have any lump or any other symptom I do not feel any discomfort while working out or doing any activity It's only the pain that keeps coming and going Please suggest what might be the reason as the pain brings down my regular energy and creates hindrance in my everyday life