I had shoulder surgery so I know all about shoulder pain. I bought a Sunmas tens unit from Amazon.com, and found replacement electrode pads on ebay. The tens unit really helps a lot when the pain just won't stop.
I suggest you have the shoulder x-rayed to find out why it hurts so much.
Amazon delivers in two days. In the meantime, keep ice packs on it, and take extra strength tylenol, and coated aspirin.