I injured my shoulder last august. i am still experiencing weakness of the shoulder, pain radiating through my entire arm, and stiffness when trying to move it above shoulder height. what could it be?

Tough to call!: We don't know how badly you injured your shoulder, and what damage was done. Obviously, it was a serious injury, since it still hurts though. You could have injured joints, muscles, or tendons! You will need to see a doc, who can diagnose the problem, decide if you need further evaluation and/or physical therapy, as well as other treatment options. Don't do things that hurt a lot till seen.