With more and more people suffering from food intolerances and allergies from foods with so many labels on that are hard to define. The best way to find out what your allergy or intolerance could be is to write a diary.
You can use them to record everything from what you have eaten, drank and any medications you have taken. Most are for three months which is long enough for the symptoms to become familiar.
My top three which are all available on Amazon are –
Food Diary and Symptom Log by Teal Bubble Books