I am honored to assist you. My answers are for information purposes only. They don’t substitute for a visit to a doctor’s office. Doctor/patient relationship is not established.
He could have type 1 diabetes melitus or diabetes insipidus.
Have you taken him to his doctor?
type 1 diabetes melitus is usual diabetes.
diabetes insipidus is s an uncommon disorder characterized by intense thirst and the excretion of large amounts of urine.
He should see his doctor to have a blood test, a urine test, a water deprivation test (if necessary), and a physical exam.
is that the only possibility ?
or any alternative or are the test by elimination
is your conclusion based mostly on the excessive thirst and peeing ? As the other symptoms do normally not occur with diabetes (well according to internet)
diabetes could cause weight loss, fatigue, abdominal pain, nausea, vomiting, recurrent minor infections, increased appetite.
diabetes could cause anxiety.
it could cause bed wetting at night.