Hi , It looks like tendon or muscle insertion problem  ,do you play some sport regularly which involve shoulder thrust like badminton , bowling , tennis or swimming ,or you have lifted some heavy thing with that arm ? There are multiple muscle around shoulder and you get pain in neck also so I think you should show some orthopedic surgeon and do MRI shoulder for exact problem determination

There isn't sufficient information to reach a specific diagnosis. I would advise you to visit the orthopedician so that you can be examined and undergo investigations such as X-Ray, MRI(if indicated) to find the underlying cause and have it treated. You will need a smooth muscle relaxant and a topical analgesic gel. The following steps may help: - Apply a hot water bag over the area that hurts after which apply the topical analgesic and massage the area gently - Avoid carrying weights with that arm - Avoid doing repetitive actions with the arm - Drink plenty of water, aim to drink 3 liters of water per day. If the problem persists or worsens visit the ER at the earliest.