Overweight, Occasional Pain In The Left Breast And Underside Of Upper Arm. Any Ideas ?

I am 29, 5 8 and severly overweight (299 lbs when I stepped on the scale this morning) About a week to a week and a half ago I injured myself at work (a box of chemicals fell and I caught it with my left arm ) There was two to three days of sharp intense pain just below the shoulder muscle, that has since gone away. The concerning one is a pain that occasionally happens on the underside of my upper arm (I can pin point it and there is no radiating of the pain) and occasionally pain in the left breast itself. I know there is a condition that makes that area sensitive to women as their cycle approaches, and it does happen sometimes. My dad has high blood pressure , my mom s is average I believe and I know I am borderline high to high. I am currently adjusting my diet to drop the sodium intake. but the pain specifically has me concerned. It seems to strike from nowhere, lasts a few seconds and then goes away like nothing is wrong. Any help would be appreciated. I do sit in front of the computer a lot, but my job has me on my feet close to 40 hours a week doing moderate lifting (Stocking shelves at Walmart).