My kids have food allergies to dairy, eggs, nuts, and some food additives (dyes, nitrates) in addition to having reactions to soy products due to food protein induced enterocolitis syndrome. This may result in diarrhea or vomiting. The "allergy" test which looks at IgE levels will show up negative for an entercolitis problem. This type of entercolitis is seen when the person can't handle soy and dairy products. Entercolitis also differs from lactose intolerance because it is not due to lacking the enzyme lactase that breaks down milk sugar; it goes beyond having bloating and gas.
I am often surprised at how many pediatric GI doctors do not even look at this diagnosis as a possibility. Sometimes the parents of the kids I work with are told to give the child soy or dairy after the IgE test shows no positive sign of allergy. I think if the parent is seeing the child in GI discomfort, then the food shouldn't be added back into the diet. The allergist doctor that my children go to is the one that educated me on food protein induced entercolitis syndrome, yet my experience is that even some allergists don't look into this possibility. I realize though that every doctor has different trainings and experiences...wish more of them new about this possibility!
Food Protein Induced Enterocolitis Syndrome - FAAN
If you've not went to a doctor for your child's digestive or allergy problems, then please do. You may want to visit an allergist if your child hasn't got better and has already seen a GI doctor. Some of my clients have even needed to go to the neurologist to rule out other problems such as metabolic or mitochondrial disorders which can have an impact on the GI system. One thing that is important to do before the doctor's visit is to keep a food diary. List out what the child ate, what time, and if there were any behaviors or digestive problems (e.g. burping, vomiting, refluxing, diarrhea, constipation, gas). If you've done this for over a week, you might be able to see a pattern and figure out the culprit. Sometimes not, but then you are able to rule out which food is not the offender!