Need help with a 6 year shoulder injury

I injured my rear deltoid doing rear deltoid flys when i was 16, i was a boxer and also weight lifting. The rear delt pain was intense as i didnt stop training for 6 months after the injury. It has been constitent pain for now 6 years and cannot go to the gym. I had pain in my what i believe my rear delt, teres minir and major and when it flares up my shoulder drops forward and turns inwards and i cannot do any shoulder exercise without intense pain and weakness. I have seen 2 orthapedic surgeons, around 10 physios, and 3 osteopaths. I have also had 2 MRI. On the shoulder and xrays. And shows nothing...... the pain is intense if i reach out in front with any weight. And my rear delt and the little muscles below my rear delt feel like there rubbing and popping and clicking all the time. I have been tjeough shoulder rehab about 15 times over the past 6 years and still the pain is consistent and i have never been able to train again. Can someone please advise me