Your symptoms suggest shoulder instability with tendon irritation, likely involving the rotator cuff and surrounding stabiliser muscles. Pain during side-sleeping and even at rest indicates inflammation and weakness of shoulder stabilisers.
Next Steps
Pain management: Icepac, ultrasound and IFT to reduce irritation.
Strengthening program: Start with isometric and closed-chain shoulder stability exercises.
Progressive rotator cuff strengthening: Theraband exercises for external rotation, internal rotation, and shoulder abduction.
Posture correction & scapular strengthening: Middle trapezius, lower trapezius, and serratus anterior activation.
Manual therapy: Soft tissue release and joint mobilization.
Health Tips
Sleep on your back or use a pillow to support the painful arm.
Avoid overhead lifting and sudden heavy activities.
Maintain good posture, avoid rounded shoulders.
Apply ice pack 10–15 mins after activity.
Be consistent with exercises for 4–6 weeks for visible improvement.