Generally the front of the shoulder feels like it was hit with a fist. Raising the arm makes it hurt worse. Turning a steering wheel in your car aggravates it. If you push in the front middle of the shoulder it hurts. Sometime the pain goes up under the collarbone.
Exercise makes it feel better, but then a few hours later it hurts full force.
Some snapping can be heard when you raise the arm up and rotate it. That is from the tendons in your shoulder that pass through a hollow cavity in the shoulder rubbing and snapping. The more you use the unstable shoulder the more the tendon swells and the more it snaps. Which intern, the more it hurts and keeps hurting. I know you want to know what the fuck caused this shit.