How Can Pain In The Right Shoulder And Arm Be Treated?

I ve had pain in my right shoulder for nearly three years. I got injured three years ago at work while using a meat slicer. I figured it was the repetitive motion that injured me. It hurts the most at night when I am laying on it. Though, it hurts when I extend or reach upwards too. Getting dressed is difficult since using my right arm is painful. The pain is dull and gets sharp when I move my shoulder the wrong way. Recently the pain has started to travel down my arm. I m hoping to find some answers.