Help needed for two year old with very low blood sugars

Patient: My 2 year old daughter is very sleepy and showing a lot of the diabetes symptoms. she had her blood sugars checked yesterday and they were 3.2 after eating. today she had bloods taken at the hospital and after eating her lunch her sugar levels were only 4.0 she is very sleepy, very irritable, drinks water non stop and urinates though at least 8 nappies a day what could this be?