That's a bad spot to have pain, this is your acromioclavicular joint, where your clavicle, (collarbone), meets the acromion process from your scapula, (shoulder blade). If this joint comes apart it is a shoulder separation, and it is a very difficult injury to recover from. Be very careful with this injury, don't do anything to make it worse, or you'll be out of action for a long time.
You will have to do most of your upper body exercises with very light weights for several months. Don't do any exercises that cause any pain.
A really good chiropractor can make certain that the joint is in it's proper alignment.
I've suffered through this many years ago, and it can be a very long process. But with light weights and higher reps, you will keep most of your muscle mass.
Work the muscles of your rotator cuff group thoroughly and carefully, this will help.
Hopefully if you take care of the problem right now, your recovery can come soon.