Allergies

We noticed he had some red bumps on his legs last night when we got home from church and this morning they had spread to his feet. He kept itching them too and telling me he's sick. Off to the doctor and his diagnosis was a food allergy. I'm to keep an eye on him for 48 hours because it will probably get worst and to give him benadryl. The doctor said the usual suspects are peanuts/tree nuts, shellfish, and strawberries/berries. I guess there is a reason Isaac tries to stick to pasta, corn products, and bread. I can't figure out what he's allergic to though. Last night the snack at church was cookies with M&M's on them and lemonade. He's had peanut butter many times before too. I'm stumped.