[Julian]

Maybe I can give you some information (you may already have this)

Shoulder pain felt in the deltoid region ( outer shoulder ) is often a result of rotator cuff pathology.

The main pathologies are impingement where the cuff gets inflammed and rubs on the acromion bone, tendinitis/tendinosis which are micro cuff tears or strains and finally cuff tear

The most common pathology is impingement associated with a painful arc at 90 degrees elevation and difficulty lying on the side at night. Common treatment includes phsiotherapy to strenghten the muscles that depress the humeral head, anti-inflammatories and corticosteroid injection. Surgery is an option if these fails.

The treatment for tendinosis is similar

Cuff tear is more serious and is manifest as weakness especially to external rotation of the shoulder which indicates a larger tear. It is corrected surgically if weakness is a major issue

You sound as if you have impingement. I would suggest you see a doctor and have a radiograph to exclude other pathology, confirm the diagnosis and arrange appropriate treatment. Sometimes rest will improve the condition but if symptoms have been greater than 4-6 weeks I would see a doctor

Hope this helps

Julian