When that 'pop' happened, that was the initial injury.
What's most likely happened since then, because of lack of treatment, is scar tissue has built up and essientally 'locked' your shoulder into one unit. This explains the pain when you raise it above your head.
This is coming from a fellow ball player, 16 years. I've injured my rotator cuff before and neglected treatment as well. It took months of slow recovery exercises and deep tissue massages before I finally felt 95% again.
I'm not sure what ligament or tendon or muscle you may have torn, but after the injury healed itself, poorly, overtime, everything healthy around it (muscles, ligaments, tendons) began compensating for the injured body part, creating imbalances and weak points.
Once that scar tissue locks your shoulder together, strength training is useless. You need to break up the scar tissue and release the surrounding area. You shouldn't be surprised how much your traps, lats, triceps, and biceps can affect your shoulder, because these are the areas that have been recruited to do the work that your injured shoulder cannot.
One way to tell if you have a shoulder injury is to take a light weight, 10 - 15 lbs, and slowly do lateral shoulder raises. If when you reach the top of the movement, you feel your shoulder roll forward or your trap shrug up, you're probably injured. This is a prime example of the surrounding areas compensating for the injured body part.
Shoulder injuries are tough to recover from because they take lots of patience. Hope I could help.

__________________
Twig? Don't wanna be anymore? Check it out.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.