answer:The only thing that you can do is take him back to the vet for more aggressive diagnostics and treatment. Radiographs or an ultrasound may provide some answers. If you aren’t satisfied that your vet is getting to the bottom of things, ask for a referral to a more advanced facility. Be careful about switching foods too rapidly – sudden dietary changes can cause GI upset, too. A new food should be introduced gradually (¼ new food, then ½ new food, etc).