I know exactly what you mean, its taken me ages to discover what has caused my problems.
By the way, food allergies and food intolerances are not the same thing! During my hospital stay I was told I don't have a gluten allergy, which I know, but I do have a gluten intolerance which is not the same thing at all.
Intolerances to foods cannot usually be tested for, and allergy testing is not always 100% effective unfortunately.
Trouble is, ones body reacts more strongly each time one consumes the offending foods, so over a number of years it gets worse and worse, until we end up in the situation that we are both in where its difficult to believe that food can make us feel so rotten.