Shoulder pain could be due to various reasons. It could be due to some trauma or due to abnormal posture. Also some problem in neck can cause shoulder pain. Detailed evaluation is required to rule out other possible causes. Inflammation could be due to overuse of muscles.
Next Steps
Advise you to please visit a physiotherapist using manual therapy approach. It can fix the biomechnical abnormalities if any. Also ruling out neck problem is important.
Health Tips
Use ice packs and avoid overhead activity