Your symptoms point to cervical radiculopathy (pain due to pinched nerves; degenerative disc disease or bone spurs pressing on the nerves). This can be episodic and do have precipitation of symptoms on specific posture. The specific posture, puts pressure on nerves. The other causes of consideration would be;
1) Bicipital tendinitis
2) Frozen shoulder
3) Brachial neuritis
4) Rotator cuff disease
5) Suprascapular neuropathy
All of these conditions will respond to physical therapy alone. The program should be daily and assisted by the physical therapist. The regimen consists of active and active-assistive range-of-motion exercises combined with stretching. Other treatment modalities such as heat and massage may help. Nonsteroidal anti-inflammatory analgesics may also be beneficial. Deep electrotherapy in the form of short wave diathermy, Interferential current, trans cutaneous electrical stimulation, iontophoresis, phonophoresis also is very help initially.
For pinched nerves of neck; following investigations would be required;
1) X-ray of the neck spine
2) MRI of the neck
3) Nerve conduction velocity (NCV) study
4) Electromyography (EMG)
Following measures would be helpful;
1) Neck care in the activities of daily living.
a) No working on computer for more than half an hour in a single stretch. Same for TV.
b) Monitors and televisions exactly in front (180 degrees).
c) Contour pillow: Should fill the hollow when lying on back or straight. Available over the counter.
2) Cervical / neck traction
3) Anti-inflammatory analgesics like Ibuprofen
4) Physical therapy: gradually increasing exercises from passive stretching to active against resistance regime.
5) Electrotherapy in the form of TENS, interferential and laser and ultrasound.
6) Local analgesic patch / ointment / spray
You can consult following specialists;
b) MD in Physical medicine and rehabilitation
Please feel free for your follow up questions.