What Causes Nagging Pain Between The Shoulders And The Elbow?

HEIGHT 5'10 WEIGHT 250 AGE 52 FEMALE - HEALTH GOOD NO PROBLEMS. MY LEFT ARM BELOW MY ELBOW ON THE FRONT SIDE HURTS LIKE A NAGGING PAIN SOMETIMES IT GOES UP TO MY SHOULDER LIKE IF THERE IS NO CIRCULATION SOMETIMES HURTS REAL BAD AND i CAN NOT SLEEP. . ALSO WHEN I USE MY RIGHT ARM THE PAIN GOES UNDER MY UNDERARM DOWN MY BACK.