What signs of hypoglycaemia is your son showing? Have you tested his blood sugar when he is having these symptoms to see if he has low blood sugar? If he sees you testing your blood sugar he might be keen to have a go on it himself.
If his blood sugar is normal then you might want to be seen by the GP to see what else might be causing the symptoms. If his blood sugar is <3.5 you should get seen by the GP to see what is causing low blood sugar.
I'm not sure what tests to look into that would be excluding. Low blood sugar is not a sign of undiagnosed diabetes as diabetes is a condition of high blood sugar. It might just be growth spurts meaning your son needs to eat more frequently. But if you are concerned, keep records of what your son is eating and when, what is he doing and when he gets these symptoms and go to have a chat with your GP to get it checked out.