What Causes Muscular Pain After Interferon Treatment?

My husband's muscles have been causing him pain ever since he completed interferon treatment for Hep C, in fact, they seem to be hardening and nothing seems to relieve it. Further, he has lost a lot of weight (almost 50 pounds) and is skin and bones now. He is a service connected disabled vet and none of the doctors seem to take the muscle issue seriously. any ideas?