We cannot diagnose your son, you must take him to a doctor.
Diabetes insipidus and diabetes mellitus share some symptoms, but are totally different conditions. This is the place to ask questions if your son is diagnosed with diabetes mellitus. I think some people here have diabetes inspidius as well and may be able to point you towards a message board for that condition. Please don't assume that information/advice about one condition also apply to the other, you need to get a diagnosis.