Hey Katie,
This disease is highly variable. The symptoms you feel are usually dependant upon the location and size of the lesions. I have had deep muscle pain usually associated with spasticity. I suppose if you have severe spasticity near a joint you could be pulling that joint well sort of out of allignment or against itself?? I don't see why some wouldn't have joint pain but I have not heard of anyone complain of this. Certainly mention it to your doctor.
Also, remember that just because we have MS does not keep us from getting other issues. You could certainly have some arthritis or other inflammation going on. Good luck.