Hello from JustAnswer.
I am sorry that you are having so many problems.
Do you have any chronic medical problems besides the back problems?
Are you taking any chronic medicines besides the Co-codamol?
I had asked for some additional information and have not heard back.
The most likely cause of an ache in the side of the neck that radiates down the shoulder into the arm would be from a problem in the neck. The most common would be from an exacerbation of degenerative disease of the spine. However, it would require a proper evaluation to determine the underlying cause.
At home, there are limited options of what can be done. One of the key home interventions would be the use of an over the counter anti-inflammatory medicine, if not already taking. The reason that I asked for further information is not only to know whether you are already taking an anti-inflammatory drug, but also to know whether there are any other medical condition or medicines that would preclude the use of an anti-inflammatory medicine.
It also would be OK to try local care to the neck, such as ice and moist heat.
If I can provide any further information, please let me know.