That's good...means you probably don't have a torn rotator cuff.
The main area for arthritis in the shoulder is where the collarbone and shoulder blade come together at the top of the shoulder(AC joint)....not in the shoulder joint itself. And just to make matters worse, there is a huge bursa under the joint that can hurt far more than the arthritic joint. So chances are, it's one of those 2 problems.
Try applying ice to the area that hurts. It takes down swelling and that eases the pain. If the muscles in the area hurt, they need heat. Improves blood flow to the muscles and reduces that pain. I frequently end up with an ice pack on the AC joint and heat on my neck muscles.
If it continues, see your doc. He/she can do a cortisone shot into that area and it will help the bursa and the joint. If and when it gets so bad you can't sleep, they can do surgery through a scope to cut off the arthritic end of the collarbone and that fixes it. Day surgery with little pain.
Hope this helps you.