Intolerances to food can happen when we can’t properly digest particular foods. Symptoms can be obvious (upset stomach, bloating etc.) after eating the particular food; however, symptoms that don’t affect the GI tract may include headaches, hives, stuffy nose, etc. A great way to find out which foods are causing intolerances for you would be to keep a food journal and record the foods you eat.
When you think you know the culprit, try cutting that food out of your diet and see if this fixes the issue. It may be that you need to supplement with a different kind of food with similar nutrients and benefits.