I suggest you might google candida as it can cause a variety of symptoms (IBS, burning mouth, depression) and even create food
allergies as your absorbtion of food
is messed up by the fungal overgrowth; basically causes
leaky gut. Also might look into Celiacs Disease, which is basically an allergy to gluten. This allergy alot of times doesn't develop or at least doesn't show symptoms until adulthood. And it can create allergies or intollerances to other foods basically by leaky gut again.