you should find a competent doctor (very very very hard to find as most do not read or follow the best books they read) doing screening for gastro parasites and yes mucus scrapings to rule out gastro parasites. Gastro parasites can cause problems all around the body. And yes food intolerance is often one of the signes....there can naturally be other reasons also, but one need to make sure one has ruled out parasites. It is all about going to a competent doctor, again very very hard to find, but yes there exist a few.
Have in mind most infection disease specialists will miss out one of the most important parasites that MUST be ruled out Entamoeba Histolytica, for this you need mucus scrapings. Do not listen to doctors telling it can be ruled out on stool samples (even PCR test), antigen test, or standard colonscopy.
Find a competent doctor with many years experience in parasites and Tropical medicine that also do mucus scrapings, if not doing mucus scrapings the doctor can not rule out what must be ruled out.
Do not accept any doctor not finding the true cause giving crappy symptom diagnose and symptom medicine. Some symptom medicines can be very harmful and weaken immune system when one need maximum immune system to fight parasite until right diagnosis given and right medicine to eradicate them. Right diagnosis is extremely important, most doctors are unfortunately incompetent when it comes to parasite diagnostics, even very many infection disease specialists.