I'm guessing he's Type 2 from the meds he's on. I was diagnosed in May and got mine down to normal levels in about two weeks. On diagnosis I immediately lowered my carbohydrate intake to less than 100g/day, and after another few weeks I dropped to between 50-70g/day.
You need to be counting carbs accurately as there's a lot of foods that are surprisingly high carb. I eat no bread, cereals, rice or pasta. I can get away with one very small potato at a meal but some people can't. Fruit and veg need looking at carefully too so that you keep to the lower carb ones.
I'm guessing you have a blood glucose meter, can I ask when you're testing your son. Initially you could do with testing on waking before each meal then two hours after the first bite of each meal, then again at bedtime.