is it just age?

I had the same problem with my right shoulder I had several sessions of physio with my Chiropractor it helped a little but after 3 goes at it he said I can feel the Arthritis in the joint it maybe that you will need your shoulder joint operated on and to see my GP. I already take a high dose of Naproxen for my Osteo-Arthritis and am waiting for a hip-replacement so I haven't done anything about the shoulder. I do try to do ROM excercises given to me by the physio but certain movements including sleeping on my side hurt quite a bit and it hasn't really improved.
You could ask your GP for anti-inflammatories they may help.
The joys of ageing eh?

I had this problem in my left shoulder mostly. I had 6-8 wks of weekly physio and it's improved but not completely gone. My GP said it was "probably arthritis" but didn't suggest further investigation. The physio asked me if I'd been diagnosed with arthritis and raised his eyebrows when I told him what GP had said. Ibuprofen helps and voltarol cream but not together.