Ask if your local reptile vet can just run a fecal test without the office fee(as in, bring in a fresh stool in a plastic bag to the vet) though they will need to weigh him themselves to give any medication. Fecal exams are usually somewhere between 15-30 dollars depending on the type of tests they run. They'll probably give him some panacure or some other dewormer to get rid of the worms. which it looks like he has(weight loss despite eating, dehydration, etc)
Make sure his hot spot is warm! He will need all the warmth he can get to get better. I would also advise against too much handling at the moment, as stress can contribute to not eating.
For the dehydration--unflavored pedialyte can be found in grocery stores and it does wonders to help hydrate reptiles. A soak in warm(not hot) water/pedialyte will help him out. His runny poo is helping dehydrate him more than usual, so we need to get that cleared up as soon as possible.
Honestly I really suspect stress and parasite load are the cause of all this mess, and once that's taken care of you should be home free.