When in doubt about something not being normal in your body, it is time to check with your primary doctor.
Go see your primary doctor and have it checked out. Could be just muscle strain from sitting in the position you sit in for work, could be something else.
Do you have any other symptoms, headaches, pain in shoulder, arm, hands, fingers? Do you have any weakness in your arm? do you have any numbness or tingling?
Fran