I had surgery for peritonitis in the past. Since then, I experience recurrent stomach pain and digestive discomfort, often after eating. I am unable to identify which foods trigger the pain. I want to rule out food-related causes and understand if this is due to food allergy, intolerance, or post-surgical digestive sensitivity. Please advise on appropriate tests such as food allergy (IgE), lactose intolerance, or gluten sensitivity, and suggest next steps.