I'm definitely not an expert, but from dealing with reptiles at the reptile shop my friend worked at, I've picked up a few things. As others have said, reptiles have a very slow metabolism. This means they can be ill for quite a while without showing it, and conversely they can take quite a long time to show signs of recovery, so if there are any encouraging signs I'd say keep trying. Also, have a chat to the vet and ask for his assesment, if the vet is not too worried then definitely see it through!