Hello
Since he is diabetic there are chances of having Frovzen shoulder,he may be experiencing night pain and restriction of movement especially above head and taking hand back behind the pocket. No medication will help him to relieve his pain and pain medication is contraindicated in diabetic conditions. He has to undergo vigorous Physiotherapy (mobilization). The treatment will be bit painfull initially but it will surely give good results.
Hope I answer the question
Regards
Dr sahil
Next Steps
Until you visit a physio use hot fermentation over the right shoulder to relive some pain.
Health Tips
As per the information provided in the question there is no past history of injury , so you can do all activity to keep the shoulder warm. avoid direct exposure to AC