What Causes Pain Under My Left Breast Around My Rib Area?

I have been having pain under my left breast, around my rib area,medially. I had an x-ray done today of my ribs, which were negative. The MD is sending me for a mammogram/ultrasound, even though I just had a mammo. 3 months ago. Of note I had found out a few weeks ago that I have a small 4mm nodule left lung base, and recently had passed a first kidney stone. is all this related? could this be a muscle strain? i also just changed Cholesterol meds to Gemfibrizol and Zocor combined. please let me know thought.