behavior vs low blood sugars?

My son was diagnosed with ADD about a 1 1/2 years ago, and does well on his medication as far as school work goes.  However, we are noticing increasingly worse behavior right away in the mornings and at bedtime.  We just saw our family physician and we increased his dose of Vyvanse, started on a low dose of Ritalin to get us through the morning bus ride, and we are going to start seeing a psycologist for behavior modification.  The doctor drew some lab work while we were in, and the results were normal except his BG.  That came back at 69 (70-100), but what is significant is that while we were in the exam room, my son ate his after school snack of a Nutter Butter (both pieces).  It was approximately 1/2 hour later the blood was drawn.  I am concerned about what his sugar was just prior to eating that high sugar snack.  He falls into the "moderate hypogycemia" (less than 55) with his irritability, anger, etc.  My question is, what are some primary causes of hypoglycemia?  (Other than not eating right, poorly controlled diabetes, etc.)

[Renee Radenberg]

Hypoglycemia can occur after a very carbohydrate-rich meal or high sugar snacks due to the spiking increase of sugar in the blood and then a sudden decrease. To help prevent hypoglycemia is to minimize the length of time between meals (5-6 small meals a day), eat an even ratio of protein to carbohydrate foods which will help to avoid high sugar increases in the blood, and eat a variety of health foods.