Re-introduce foods one at a time
Under the direction of your doctor, you will begin to add the potential allergens back into your diet, one at a time.
You may start, for example, with bread. If you eat a few slices and symptoms return, you can be pretty sure that one or more of the ingredients in bread is the culprit, for at least some of your problems.
If you, however, have no returning symptoms after eating bread for a few days, then you may assume that you do not have a gluten intolerance or allergy. Time to move on to the next potential allergen.