I broke my shoulder badly in a motorcycle accident in 1977, developed avascular necrosis and arthritis, had surgery in 96, partial replacement in 04 and full replacement in 2012. My soft tissues are "thin and in extremely poor condition" according to my surgeon and I have extensive scar tissue throughout the deltoid and rotator cuff muscles. I have had severe muscle spasms and pain since the early 90s and have tried a variety of treatments and therapies.
What has been the single most helpful thing for me has been a hot tub although it must be a top of the line model because I have to have very powerful jets in a position to massage my shoulder area. Being able to use the hot tub, especially before bed, kept me functioning for years and has been an incredible help during recovery from my surgeries (getting in before doing my physical therapy).
I will point out that a lot of the pain that seems to be joint pain can actually be from soft tissue. Since I have a full joint replacement, I can have NO pain from the joint since it has no nerves but I nevertheless have pain that certainly feels like it is from the joint. Getting the muscles to relax, though, provides a clear improvement in pain levels.
I have also found long-lasting heat packs helpful as well as a TENS unit (up until I had partial joint replacement). A relatively new product (for me) that helps is Lidoderm pain patches.
Improvement in posture, sleeping in a partially reclining position (and anything else that improves sleep) and other general pain management techniques like meditation, distraction and relaxation are also helpful long-term.
I have other pain issues, including foot pain from structural birth defects (I am 54 yo). In my experience, you have to try and keep trying until you find the things that work for you. Doctors and therapists are certainly helpful but the fact is that there are so many variables in any given situation as complex as ours that they don't really know what your long-term prognosis will be. Even if you are told there is nothing more they can do for you, that doesn't mean that your pain will never get better. Pain is, after all, a perception as well as a signal down a nerve and that perception can be changed. Keep trying, learn about your own body and keep trying. Then keep trying some more.
I wish you the best of luck.