Shoulder pain is a common complaint. The causes of the pain range from minor to very serious. As you suggest, there can be serious causes which require evaluation. I would recommend that you see your primary care doctor
to have this evaluated. If needed, he or she could refer you to an orthopedic surgeon.
Inflammation of the muscles, ligaments or tendons is the most common cause of shoulder pain. This inflammation can occur due to overuse or due to minor injuries. This occurs in essentially everyone who overworks their shoulder muscles, and certainly can be worsened if using it without a warm up. This may be what is causing your pain.
If inflammation persists, it can cause tearing or partial tearing of the muscles. The rotator cuff is a collection of muscles in the shoulder that is often damaged. These four muscles are commonly hurt is active adults. Pain at night is commonly associated with rotator cuff injuries.
Nerve impingement in the neck can also cause this pain. This is caused by degeneration of the bones in the neck. This is less common in people your age, but possible.
I would recommend that you see your primary doctor. A quick evaluation can be done to assess if there is severe damage. If needed, a MRI
may be done, but often this is not necessary. Good luck!