What Causes Shoulder Pain While Bending The Elbow?

Hello , I'm a 28 year old male suffering pain to the back of my right shoulder. The pain occurs with the movement of washing my hands. I can lift my arm in all sorts of directions pain free. When me elbow is bent and I am pushing down the pain occurs. The more my elbow is bent the more severe the pain is in my shoulder. Also it hardly takes me any pressure for the pain to appear. THanks.