Hi, Welcome to Health care magic forum.
As you describe, you are definitely under weight, and needs a treatment.The reason may be the genetic or some chronic disease, or mal absorption.
I advise you to consult a physician for diagnosis and treatment .
I usually prescribe to my patient with such symptoms injections of
anabolic steroid, enzymes, multivitamins, and
protein supplements.
Take more of calories, fats, fries, ice cream. Also take more of green leafy vegetables, pulses, sprouts, and protein rich foods.
Try to sleep for more time,practice early to bed and late to rise. If possible try to sleep for a while during day time.
Wishing for a quick and complete recovery. Thank you.