Why right shoulder hurts alot when i sleep and lye down on the side! Please help!

Tight back muscles are causing that to happen. When you lay down it changes the pressure points in your back when you are laying down, for the pain to happen. To get rid of the pain you have to free up the muscles in your back and here's how to do that:
Back:
(do from a sitting position)
Place your left hand on your left leg next to your body. Place your right hand over your left shoulder, fingers over the back and the palm in the front and firmly pull down on them and hold. After 30 seconds slowly lower your body forward and to the outside of your left leg, keeping your left arm fairly straight as you do. When you reach your lap remain there for another 10 seconds, release the pressure but rest there for another 30 seconds. Then reverse your hand positions and do your right side.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.

you may have bruised it somehow or twisted a mussel I have done that sort of thing before. As you have had it for a while and it has not gone I suggest you go and see your doctor about it.