What Causes Pain In Arms And Behind Shoulders After A Physical Task?

Hi Dr. I work in the auto industry , i am a 59 yr old female , I assemble parts for the steering column, requires back and arm muscle movement. I also at times lift baskets of parts approx 25 to 30 lbs. I have been experiencing for a few months now, back shoulder to left arm ( back of arm) down to elbow, painful below elbow to pinky finger. at times pain under arm and into breast. turning my head left causes me pain. I've tried wearing arm ( elbow) straps, bands. Not much help. sleep with my arm down on my hip for most comfort. Any ideas? Had a few vicadin left from knee scope they don<'t even seem to help with the pain. Thankyou! Juliet