Hello !!!
I can understand what you might be going through. But don’t worry.
Every problem has a solution.
Firstly we need to differentiate wether the problem is coming from your back or shoulders.
Mostly this is a case of cervical disc disease and as you say tou lack arm strength , it needs evaluation. It is considered one of the red flag signs and needs decompression is serious.
Next Steps
Consultation is must to know the exact grade.
Which part of neural system is affected has to be evaluated.
MRI of cervical spine with spinogram must be done