Too much phenylalanine? Should I be worried??? Please help.?

Today when I picked my son up from daycare, he was complaining of a stomach ache. Since stomach aches are so common in children, I thought nothing of it. Then he began throwing up. I called the daycare soon after to see if any other children had come down with or been recovering from the stomach virus, and they told me no. I unpacked his book bag and found a tin of Icebreakers mints, which were almost all gone. I asked my son where he had gotten them, and he said one of his friends at school gave it to him. I asked him if he had ate a lot of the mints and he said yes. The mints have phenylalanine in them, should I be concerned? My son is 4 and is otherwise totally healthy. He seems to be acting okay, he is just complaining of not feeling well but can't seem to pinpoint any exact pains or problems. Any advice or am I over reacting?