Has there been any frantic desire for food along with those symptoms? If
so, it could very well be diabetes. My now 17 year old has had it for 5
years now (two shots a day!) and his initial symptoms were never ending
hunger, water drinking, and huge urine output.

On the other hand, my mother's 15 year old had similar symptoms but with
this added symptom: his pink nose and pads became very pale. Turns out his
kidneys were failing, but with a switch to a renal support food, he's been
doing remarkably well. (My 17 year old still acts like a kitten from time
to time, though a lot slower, so he's done well on insulin and appropriate
food.)

Given the age, you probably would be best served by a diagnostic blood
test.

Good luck,

Frank