The home remedy I mention below works definitely (sp) an encouragingly large amount of the times. Butit does not work with most parasites. But sometimes an ig has a very virulent, strong gram-negative bacteria that has to be killed off with antibiotics.
When antibiotics are used, all the gut flora is killed off, and needs to be replaced right away as I explain below. A prolonged period of lack of gutflora takes the form of lack of appetite and loss of vigor, plus the tendency to pick up another bad gut flora or fauna.
Has anyone suggested that you have a possible home remedy at hand? You may buy live gut bacteria in the form of square damp cakes from health food stores. Although they are balanced for humans, I've had a lot of positive results by feeding that stuff. You can get a balance more suited for reptiles from avian (bird) vets, if there are any close enough to you. They are stored in small damp square cakes in refrigerators to keep them alive. Feed 1/4 tsp every other day for 14 days, until the beneficial organisms crowd out the bad ones.
The bacteria are one of the possibilities. Possible gut parasites are the other possibility that has to be found in a fecal sample sent to a lab. Some of them are tiny. Not all can be found in your vet's office.
The "crowding out" phenomenon is very interesting. It's a fascinating read.