A cousin of mine and a family friend both suffer from a Vitamin C (citric acid) allergy which means they can not eat anything like tomatoes, oranges (any citrus), etc. They both get rashes, but as they grew older the reaction worsened, and both have been hospitalized after they swelled up so bad that their eyes, throats and airways swelled shut. They also both suffered severe intestinal/stomach disturbances with those reactions.
My cousin always had mild symptoms such as you're describing until he shot a commercial for Pillsbury. They used to sell a premade short-cake and he had to eat something like 20 strawberry shortcakes for a commercial shoot. He almost died from the strawberries.
The family friend always sufferd minor symptoms until she was thrown a surprise party and wound up having to eat a big plate of spaghetti, tons of other tomato sauce based dishes, a strawberry torte, and some sort of fruit punch and just like my cousin almost suffocated to death after her face and throat swelled up during the party.
Until you hear more from the doctor, I'd be very careful about serving your child any foods (fruits high in citric acid) in the same vein as tomato (which is considered a fruit). In both of these cases, the people always had mild symptoms until some unusual circumstance came up where they ate more than a small amount of citric acid.
Hope this food for thought helps.