Feeling very tired and losing a lot of weight after a long course of antibiotics may be due to changes in your gut, poor nutrient absorption, or the impact of your new egg allergy on your diet. It is essential to see a doctor or gastroenterologist for tests to assess nutrient deficiencies, thyroid function, and overall gut health. Meanwhile, focus on eating a balanced, nutrient-rich diet with protein and vitamins from foods you can safely eat, and include fibre-rich foods to help your gut recover. Your doctor may also suggest probiotics or other ways to restore healthy gut bacteria. If fatigue or weight loss continues, further medical evaluation is needed.