you need to get what's known as an MR-Arthrogram...this is where they inject dye into your shoulder and then put you into an MRI machine...they can tell by the way the dye spreads if there is a tear or not....
if there's a tear, you'll most likely require surgery...
if not, you may need rehabilitation, pain meds, rest, etc...
i had a shoulder prob a while back, and glucosamine/chondroiton/Msm helped a little.
good luck with your shoulder, i know it sucks.