I am a double board certified US doctor and I will help you with this, providing correct and safe answers. Use reply as needed.
In fact there is nothing you should do to try and fix this until you have a diagnosis and the therapy assessment.
You can hurt yourself if you do.
The safest thing is rest, using a sling if needed, heat and cold applications, which ever helps, and anti inflammatory medication temporarily.
You need an orthopedic exam as well...if not done.
This can be a torn muscle, particularly in the shoulder or bicep.
It can be something more serious, such as a torn labrum in the shoulder.
Or even a herniated disc in the neck.
That needs to be found out.
OK, so you might have more questions or want to give me more information: Please use reply to expert if you have further questions. Also, please click a positive rating [hopefully excellent (5)—that’s how we are paid, per rating]. If you forgot something, just use reply and come back. I am here http://www.justanswer.com/medical/expert-dr-thomas/