a cortisone shot and laying of completly for several weeks helped mine the first time , had toget surgery the next time. I had an Distal clavical AC impengment for whatever the fuck that means.
Basicaly it was described to me as calcium buildup putting pressure on the bursa causing it to inflame and it would recure as long as the calcium buildup was their. the dr X-rayed and MRI'ed the other should and said we may as well do them both cause it was gonna have the same problem , that shoulder (left one) had never had any pain only my right one so I told him hell no just the one , he fixed it , had minimal down time and it was good as new 6-8 weeks later , for months after getting back in the gym steady the left shoulder started to act up , limped along for a year with another cortisone shot then had it it done.
my Dr said that the bursa was their and needed especialy if I were gonna be stressing the joint with lifting so he diden't want to remove it , only removed the extra buildup , I have since cut out any barbell benching and obly do dumbells , mostly only on light incline and decline , zero issues and my strength and size is better than it ever was