hi i had gone through your query and understand your concerns. i would come up with the possibility of ALLERGY is the underlying for all your sufferings including underweight. -usually the energy came from food absorbed from the intestine into the blood.the blood contain oxygen ( oxygen acts as a vehicle to the Hb)which carries the energy throughout the body. -if a person suffering with allergy has less amount of oxygen in the blood which cant be sufficient to distribute the energy leads to malabsorption and is the cause for your underweight. treatment option; i advise you taking Homeopathic medicines gives safe and permanent cure for your complaints consult your local homeopathic physician for correct diagnosis of the case and remedy to fit your complaints I hope this is helpful for you, thank you