My 25 Year Old Diabetic Grandson Is Urinating Excessively Causing

My 25 year old diabetic grandson is urinating excessively causing him to wake up many times at night to urinate and very little comes out. He is very tired all the time because of this. He wears depends to avoid embarrisment and sometimes goes through the depends causing more embarrassment. Doctors don't seem to know what is wrong.
Are you able to help?