pain in shoulder

I have pretty severe pain in my shoulder when I try to riase it perpendicular to my body (as if making the wings of a plane).
It does not hurt as bad if the end of my arm is in the plane of my body, but if I have my forearm in front of my body and try to raise the whole arm from the shoulder I have the severe pain.
I can not perform a motion such as pouring a pitcher of water, and have trouble shifting my car. I was told it might be biceps tendonitis, but have no pain in the front of my shoulder. Any ideas on what this could be?