[tincup2004]

Where exactly on your shoulder? If it is in the front then it could biceps tendonitis. If it is more on top around the shoulder blade, then the rotator cuff may be irritated. Does it act up only when you golf or does it occur outside of golf as well (ie work related)? It is possible that the horizontal hinging (full roll) may be causing your left arm to externally rotate with more force than it can handle. Your PT should be able to pinpoint the root of the problem. How is your PT coming along?

Other things to consider are how many balls do you hit during practice? Are you hitting off turf or grass? How many rounds of golf per week? Have you had any previous shoulder injuries? If you are hitting, try angled hinging and see how that feels.