Bearded dragon sick, Parasites?

My daughter has a bearded dragon, he's now almost 7 years old & has always been healthy. For the last couple of days though he has lost his appetite & seems to have had sudden weight loss, his eyes are also sunken & he is very lethargic. We have taken him to two vets who won't treat because neither are experienced in treating reptiles. Our nearest reptile vet is miles away. I've been searching for answers on internet bearded dragon care sites & it seems pretty likely to me that he may have parasites, perhaps caught from the crickets which he eats. I am really worried about him, as is my daughter & I was wondering if there is anything we can do to help him until we can get him up to the reptile vet. We've bathed him to hydrate him & still trying to feed him mushed up vegetables, his appetite though seems completely lost. Many thanks in advance for any answers