I too weightlift and can appreciate the problems that you have come across.

Although I am not entirely sure as to what your diagnosis is, from what is being mentioned the ball or head of humerus (long bone of the upper arm) is not sitting within the glenoid fossa (part in which the head of humerus sits in like a fist in an semi-opened hand).

Firstly could you tell me what your workout routine has predominantly been for the past little while (ie. how much bench press, arm work etc.) and when you noticed the problem.

I think if you have been provided exercises before, they probably needed to be progressed. If you have been completing the same exercise for so long the 'training effect' even for the small muscles would be diminished significantly. I am surprised you have not been re-assessed and given a progressive plan of treatment.

Finally, you will need to be patient no doubt, because it takes some time for muscls to be retrained as stabilizers, something that your pec major and larger muscles are probably compensating for at this time