Well, at the ripe old age of 34, I'm dealing with arthritis in my shoulder and spine. Every gig = severe pain and discomfort the night of and day after. I've tried finding extra wide straps to alleviate some of the weight on my shoulder but no luck thus far. I'm a decent sized guy but my basses seem too heavy any more. My jazz bass is a hair over 10 lbs. I need to find a lighter weight 5 string bass or some other solution. Any suggestions?
Play seated; your leg will support the bass. I prefer a stool instead of a chair so there is nothing to hit my elbows.
Get some therapy beyond just taking pain pills. I'm a licensed acupuncturist; I treat arthritis every day. It's extremely helpful, but you have to see someone with real acupuncture training and experience -- not someone from an allied health field who took a few seminars in it. I also have arthritis, in my right hand fingers, and playing can tear me up. Acupuncture really helps; one session usually straightens things out for several weeks.