What Causes Pain In The Arm?

Right arm hurts, can hardly hold coffee pot to pour. When I get up in the morning, it hurts to straighten it. Its been hurting for a month. The pain seems to come and go, but when I turn my arm sideways it hurts like someone hit me with a hammer. I am going to go to a doctor as soon as school is out, I teach and dont have any more days left right now. Help??