Well...your first big problem is that your asking for advice on shoulder exercises and completely ignoring the rotator cuff issues. So pretty much any and all shoulder exercises are going to cause inflamation and further impingment in your rotator cuff. The tendinitis (Im guess is what it is) will get worse and if it isn't fixed by rehab/physio you may require surgery. So...what can be done? Obviously you have a an imbalance where your chest is stronger than your back and causing your shoulders to be pulled forwards. So what you need to do is strengthen the rotator cuff muscles (and probably also the posterior deltoids and other back muscles as well). The best exercise for this is a dumbell raise. Its done laying down on a bench with your arms extended straight upwards (no elbow bend) with your palms facing towards each other. You then just raise your arms upwards slowly as high as you can and lower for a count of 4. This should probably be done w/ a weight you are comfortable w/ for about 15 reps. Other good exercises are rear dumbell flys (do them one arm at a time slowly) or w/ elbows bent (I call them chicken wings). Just whatever you do stay away from upright rows. I got tendinitis in my shoulder when I was 17 doing those. Another big thing is constantly thinking about your posture and setting your shoulder girdle (raise shoulders up towards ears, pull them back, lower them down). That should help.