Welcome to Ask A Doctor Service, I have read your question and understand your concern. This is what I suggest to you. Based on the chronic nature of your symptoms I am suspecting you have a food intolerance of some sort. Undergoing an elimination diet under the supervision of a trained Nutritional Medicine Dietitian or Physician may assist you in identifying offending foods causing malabsorption, stool problems, weight issues and feelings of weakness. I also suspect multiple nutritional deficiencies of which protein may be one and vitamins/minerals almost certainly. I wish to advise you to take a complete vegan multivitamin that is hypoallergenic and free from wheat, gluten, milk, soy or additives of any kind. For identification of some of the potential nutrient deficiencies I recommend seeing a physician and getting a complete blood cell count done for anemia with iron, B12 and folic acid studies. A TSH to check for high thyroid function might also be in order. If these lab values are off they will need to be specifically treated in conjunction with a high protein, high calorie meal plan. A qualified dietitian can help you with a high protein, high calorie meal plan. Such a plan would emphasize small, frequent feedings high in nuts, whole grains, whole fat milks/cheeses/yogurts if you include these in your vegetarian menu. Including avocados (a high fat fruit), olive oil liberally, olives will also help put weight on. Essentially, anything with good fats such as nuts, olives, avocadoes, coconut milk, nut or olive oils, nut butters will all help as fat has 9 calories per gram as opposed to carbohydrate and protein which only have 4 calories per gram. I hope this gives you some ideas of where to get started. It is not good to treat the symptoms without identifying the cause. We must determine the cause of you low body weight to best treat you. Warm Regards, Kathy Shattler, MS, RDN