I had to go see a doctor for the same reason last year and he just took some x-rays and gave me some anti-inflammatory pills to take. My joints were just a little inflamed. I think that the pills probably helped. Also, did a few exercises to build some muscles around those shoulder joints. My shoulder rarely pops now. This just helped me. It probably only took 2 or 3 months (I think, can't quite remember).
How long have you been doing the stretches, etc? I'm certainly no expert. Just wanted to say what helped me. If you haven't gone to see a doctor, maybe you should.