It sounds as if you may be experiencing some cervical issues. It probably wouldn't be a bad idea to have your back checked out.
When the cervical area in the back is having issues, especially when nerves are involved, it can produce a numbing effect of the arm and hand itself.
I experienced the same thing and the Doctor found that I had a herniation at level C5-6.
Like Tuck said, have it checked out....
Please take care,
Molly
Hello and welcome to the Pain Management Forum. I am sorry to hear about your pain.
There are a multitude of conditions that could be causing your discomfort. I think you may want to see your PCP and request a MRI. It may simply be from over use and your muscles and surrounding tissues are fatigued. If it is bothersome a MRI should provide you with definite answers.
Others will post with their suggestions and information. Good luck to you and take care.
Peace, Tuck.