Melanie,
The RA for your nephew should be ruled out too. My concern is that there could still be an underlying autoimmune process occurring. However, another consideration is high oxalate. Oxalates are known to cause crystal formation that can lead to joint pain. It would be unusual though to have obvious swelling of a joint without also having urinary pain too as much of the oxalate crystals are excreted through the kidneys. I would suggest doing an Organic Acids Test from Great Plains. Also, food sensitivities should be ruled out as well. Great Plains has the Food IgG (dried blood spot) test. Both oxalate and food sensitivity are associated with fibromyalgia.
Sincerely,
Dr. Woeller