This is common, and may be distressing to parents. You may need to get creative with your daily menu. While your baby won't be in danger if he eats only peanut butter and jelly sandwiches for a few days, it obviously doesn't give him all the nutrients he needs. Many babies love to dip finger foods into sauces or dressings. If your son likes bananas, try giving him a small bowl of yogurt to dip the banana in.
Milk protein is a common allergen, along with peanuts, citrus, wheat and corn.
If you have a history of allergies in your family, you may want to introduce small portions of these common allergens and watch for a reaction. Check with your pediatrician if you suspect an allergy. We live in a fast-paced society. Making home-cooked meals every day may not be feasible for every parent. But, fast food isn't healthy for baby.