Two days in a row, listless and lothargic, will not eat(at all) or drink(much...), took to vet who did fecal test and blood test, fecal negative, blood test very, very slightly low sugar, gave a dose, sent some home with me, gave dose at home then one this morn., still listless, will not eat or drink, have changed food twice so far, 1st was "Veterinarians Formula", second was "Royal Cannin", both dry...WHAT SHOULD I DO?