Hello!
As you have pain also in shoulder and arm then it sure is due to cervical vertebra issues.
Start taking pain killers, consider hot fomentation and massage with diclofenac gel.
Consider steroid shots and conservative treatment such as lifestyle modifications by following proper ergonomics in your daily living.
If it does not help then you have to explore options for surgery.
Take care!
The shoulder pain could certinally be caused by your cervical spine damage. The nerves that come out of C5-C7 go into the arm and shoulder, so you are making a very valid assumption in thinking the 2 are connected. I hope your fusion goes well, be dilligent about physical therapy because it will make your life so much better in the long run. You can try light stretching in the mean time, ice or heat, and ibphrophen to help with the arm pain. Good luck! Hope this helps.