Dave, it might be good to be checked out by a rheumatologist...one that treats fibro patients. Be sure before you make the appointment since there are some doctors in the Dark Ages when it come to fibro. They would be able to give you a more accurate diagnosis.
Sometimes with fibro it feels like you have arthritis in the joints but the joints are moved by muscles, tendons, and ligaments and fibro does affect them. So maybe the muscles are hurting when you move those joints. We are just guessing here. That's why I suggest you be checked out by a doctor.
Sherrine