Sometimes that doesn't work, allergens don't always trigger the same response, or the same severity of response with each exposure. It's sometimes just better to cut out a class of foods for a few weeks and see if that solves it. The reintroduce it to see if the symptoms return. Then cut out another (overlapping) class of foods and monitor symptoms. Start to narrow down. Sometimes the classes of food that, when cut out, eliminate the symptoms can be false positives as it's one particular food in the class, or one ingredient in the food. My sister-in-law is allergic to peach skins, but can eat peaches just fine.
Maybe try a different doctor. Maybe keep a diary of what you eat. See if there is something in particular the make it worse.
We had to do it for our kid to see if they are allergic to certain foods (since my wife is).