My dog is lethargic, vomiting, and not eating. What should I do now?

Thanks for using Petco Pet Education Center, formerly Petcoach! While some dogs are allergic to eggplant, most dogs tolerate it just fine and I suspect this is not necessarily the cause of his symptoms. Vomiting can be observed with conditions such as gastroenteritis, pancreatitis, dietary indiscretion, gastrointestinal foreign body ingestion and obstruction, among other possibilities. For this reason, I highly recommend that you have Voldemort evaluated by a veterinarian for further assessment and treatment as soon as possible as I am afraid he is likely becoming dehydrated. They would be able to check for these possibilities and also check his hydration status and give him medications to make him feel better. There is not much you can do in the meantime other than keeping water available at all times and not feeding him anything else until then. Good luck! I hope you find this information helpful.