Upper to middle back pain and Sturnum pain

I play music for a living (guitar and a harmonica rack like Dylan or Neil Young use).
My neck is always bent down in an awkward position (while playing harmonica) and my arms are wrapped around a guitar many hours each week. After years of playing I am now having problems with mid to upper back pain and pain in my sturnum.
I understand the upper back pain, but the pain in my sturnum is confusing.
I’ve been told that this is all related.My Chiropractor has me on the “Cox Technique”. and I stretch and work out daily. Do you have any suggestions?I’m mainly concerned with this sturnum pain.
I feel it mostly in the morning and it seems to fade away after I shower and stretch.
Thanks. TB