Since head and neck MRI is ok, what you have is probably Scalene Myofascial Pain Syndrome. When scalene muscle is the cause of pain, the pain is referred from neck to (either all or a combination of) chest, inner lining of scapula (shoulder bone), shoulder, posterior and lateral sides of the arm right up to the thumb and index finger. When this muscle shortens, this can press on brachial plexus (bundle of nerves and blood vessels in the armpit) and the subclavian artery and can compress or irritate these structures and cause symptoms such as abnormal sensation, cold extremity, spasms of pain, and lymphedema (swelling of lymph channels causing swelling of arm or leg) in the involved extremity. Treatment is by physiotherapy that involves indentifying the trigger points, and massaging them, and other exercises to relieve the muscle tension.
The other possibility is carpal tunnel syndrome or cubital tunnel syndrome. Nerve conduction studies may help diagnose this. Sometimes, the nerve impingement in the neck may eb due to wrong posture. Use a hard bed to sleep. Avoid a pillow. Roll a towel and place it under your neck while sleeping on the back and between head and shoulder when lying on the side. Initially this will be uncomfortable but with time the acupressure will work. Use an analgesic cream or spray. Anti-inflammatory drugs and muscle relaxants also help. Also, you must improve your posture while sitting and working. Manual therapy, traction, cervical collar, neck exercises etc should all be tried as all these can help relieve pain.
Since a confirmed diagnosis cannot be given on net please consult your doctor regarding all these possibilities. Hope this helps. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.