It is very rare for a child to be allergic to breast milk but it can happen. If he actually is allergic he might not be producing the enzyme necessary to breakdown the lactose. Breast milk, cows milk, goat, sheep, soy, rice, etc are NOT the same. Animal milks are really specie specific. That really means, what is perfect for a cow might not be so perfect for a human, etc. Some of the things we call milk are not really milk so be careful. If your child has true food allergies DO NOT add any bananas/cereal/etc. to formulas. You should have seen what my child looked like the first time he was given some and he was about 1 year. The hives were not pretty.
I do advise you to find another doctor. Make a pest of yourself until you get the answers you need. (My doctor knew who it was by the screaming child in the background.) Until you find one, try feeding small amounts more frequently (an ounce or two at a time), let him sleep in an infant seat, burp well. Have you tried to change your bottle? Some of the ones on the market allow for a LOT of air to be gulped with the milk.