Upper back muscle spasm

[Taharry]

Recently, upon waking, I am experiencing a muscle spasm in my left upper back, justbelow rib bone. Stretching, standing upright, breathing deeply or rising left arm increases pain.
Bending alleviates temporarily, and pain lessens throught the day. However, it will return every morning.
Pain is now going into the second week. I've not strained recently, nor caused injury.
I do however work at a computer daily for lengthy stays, own my own business and am under, at times, a lot of stress.
When evening arrives, the pain radiates to front of chest under breast bone.
I'm not sure what specialty physician to begin with.
Currently evacuating fromTexas Gulf Coast.