Hi welcome to Health care magic forum.
Thanks for calling H.C.M.F.
Left rib cage
always suggests gastric irritation, pancrias pain, some times due to cervical spondylosis
. Because the pain is associated with shoulder pain
, and all the tests are negative for other possibilities, it may be definitely spondylosis only.
I advise you to consult an orthopedic surgeon, for diagnosis and treatment. You may need to have M.R.I. neck for confermation.
If it is negative you can go for gastroscopy, to rule out gastric problem.
Wishing for a quick recovery .