Child with food allergies, help?

I myself am allergic to peanuts/tree nuts, and my son his allergic to dairy, eggs, peanuts and tree nuts. We found out at around 6/7 months old. He turned 1 a few days ago and I'm struggling on foods and meals I can give him to ensure proper nutrition as he's a little behind on the growth chart in weight. He had his 1 year old checkup yesterday and his doctor didn't quite seem to answer my questions on nutrition completely. What do you allergen parents do for your children with maybe these same type of allergies?