I am a mother of a one and 1/2 year old boy who has many food allergies. His father is Celiac which means he cannot tolerate gluten, a protein found in wheat, oats, barley, rye, spelt, and kamut. He also has problems with casiene, a protein found in dairy. Soy, eggs, and peanuts are also on the taboo list. What do we eat? Lots of greens, rice, quinoa, seeds, beans, and fish. Non-glutenous grains include millet, quinoa, buckwheat, and amaranth.
Reactions to all or any of these allergens can vary, but generally include bloating stomach, flatulance, diarhea, dark circles under eyes, migraines, lethargy, stomach pains, constipation, irritability, mental "fogginess", etc.
The easiest way to test for allergies (Hah! it's never easy!) is to remove a suspected food from your diet until symptoms improve. You may have to remove several foods from your diet to really start to feel better. After you notice an increase in energy and a decrease in the symptoms listed above, slowly reintroduce a suspect food into your diet, one at a time. If you have an immediate reaction to the food, do not eat it for a day or two, then try again. It's a hit or miss technique, but it's the best way to figure it out. recovery is a long process. My husband has been gluten-free for almost two years now, and he is still at sub-optimum level of health. It is also very difficult to get diagnosed because it is relatively unknown in the Americas (though well-known in Europe). There are many resources on the web.
Good luck, and hang in there! So many people would rather ignore their allergies than cut out so many food options. We cannot eat at restaurants due to the likelyhood of contamination. We buy organic and cook all our own meals. It isn't easy, but it's worth it. The alternative is far too unpleasant.
I hope this is useful to you. Feel free to email me any questions. I only have my own experience and research on which to base my opinions, but I'd be happy to help in any way I could.