Are you sure it doesn't matter what you eat? If you eat just tofu, hard boiled eggs, or some other food that has virtually no carbohydrates, do you still feel weak? How soon after eating do you feel weak? Do you have any other digestive symptoms? What do you typically eat? Do you tend to eat small meals, or a smaller number of meals that are large? Do you take vitamins with your meals? It is hard to try to figure out what is going on without more information.