I'm having pain from my left armpit, going around my shoulder blade, and up into my neck. it comes and goes and sometimes radiates into my lower back?

Many causes: your symptom may be reflection of multiple causes. The most risky one is heart. #2 is many musculoskeletal disorders that might be associated with type of work you do. You need to see your PMD to sort it out and give you right treatment.

This description is: consistent with a radicular pain, i.e. pain originating from pressure on nerve fibers exiting the cervical (neck) spinal cord. Accurate/effective diagnosis/treatment can be difficult to find & bad help can not only not help but make things worse. Suggest find a physical therapist who is expert in Robin McKenzie evaluation & self-treatment techniques. Unlikely an internal mediastinal organ issue.