Get yourself tested for food allergies. It can help you know what to avoid for sure. That said, my allergist is a big believer in 'if it ain't broke, don't fix it' i.e. if something is not giving you a problem, don't worry about it, and if it is, don't eat it (even if the test says you can). Also, do a Google search for elimination diets. That's where you start with a very safe base of non-allergenic foods and add in ONE new food at a time every couple days or so. See how you take it then make a decision on whether it works for you. I know that for me, I did not test as allergic to dairy, but I feel better when I don't eat it, so I don't eat it. And there is something about loaf bread that does not work for me----crackers are fine, flat breads are fine, but something about loaf bread does not agree with me.
Aside from that, I have confirmed allergies to tree nuts, green beans, flax and corn. These all developed as an adult. And I have a related issue with the tree nuts where I sometimes react to certain raw fruits (this is called oral allergy syndrome and is common with nut allergies, I can have the fruits cooked with no problems). I had a very scary reaction to a raw apple once. Quite alarming.
The big issue is prepared foods---corn/corn starch/corn oil is in a TON of stuff and some people with corn allergies react while others don't. I am okay with citric acid, and with baking powder if it's a small quantity spread throughout a whole recipe. I know of others who are much more sensitive than I am. But I do react to corn starch as a rule and I have to read labels carefully to avoid it. I also have to make time to prepare my own food as I cannot buy many kinds of frozen or prepared ones.
allergicliving.com has an excellent forum, and a good magazine they put out. Good luck!