Hi,
It seems to be a cervical spine (neck) nerves irritation since it causes symptoms like arm numbness and shoulder blades. Treatment options include cervical collar, pain killer etc. Please consult a neurologist for a better insight. Hope it helps.
Maybe you are not having these symptoms when you are running because of the positioning of your arms vs walking.
I would recommend imaging, i.e. MRI and a Neuro consult. Sounds like a possible pinched nerve.