I would suggest checking in with an Orthopedist - it is possible there is something medically specific there and an injection would be of help. Or a series of gentle PT movements to strengthen the shoulder area.
I would also suggest treating your playing as an athletic venture - don't play until you hurt, but play until just before that and stop. You might be able to build lengths of playing over time. Do lots of standing up, stretching and moving around between short bursts of playing. We are designed to be creatures of movement. Vary your playing positions - even consider standing at times to play. Two short comfortable sessions are better than one long session that creates pain. Consider alternating what you do by days - stand one day, sit another, have several different methods of raising the guitar, raise/lower chair height, etc. Breaking your playing up in short bursts may also let your brain process the new bits in between playing sessions - latent learning.
I would also suggest a book, Pain Free by Peter Egoscue. A lot of equestrian types (we've been dumped over the years) like his methods for reducing chronic pain - very gentle series of positions you use to align spine depending on where it hurts. I worked in the IT industry for many years and also used his techniques to overcome shoulder pain due to a combination of too much mousing and a horse injury.
Playing is so enjoyable, I hope you can find a way to continue comfortably. I can certainly empathize as I was hit by a truck while crossing a street a few months ago and have been frustrated by my inability to play, but am doing what my Ortho suggests and hope to return soon. (I keep reminding myself I am glad to be walking, talking and making sense.)
Good luck. Let us know what works/helps.
Last edited by a human on Thu May 08, 2014 7:03 pm, edited 1 time in total.
1965 Krempel Classical (660ish mm)
The rest come and go.