When my daughter was first diagnosed and started on insulin she ate like a horse. She had lost quite a lot of weight very quickly and once the insulin made her feel better she ate to put back on what she had lost. The doctor did warn me about a much bigger appetite for a few days or maybe it was even a few weeks and he was right. I remember being quite concerned that she was going to get fat and was quite relieved when her appetite finally returned to normal. Is your son maybe experiencing the same thing and with eating more than usual perhaps this is a side effect?