HI Greetings from Dr.Divakara.P Thanks for posting your query. Before going to the treatment we need to diagnose the cause of your problem as treatment depends on the cause. I need to know about your parents weight and your siblings weight to check whether your low weight is genetic or not . Don t jump to conclusion that you have Hypopituitarism . It is a rare condition , first let us check for common conditions that can cause inability to gain weight. Common causes are Chronic Infections , Malnutrition , Malabsorption , Thyroid Diseases , Diabetes . I advise you to get evaluated for these conditions first and if everything comes out normal then we can consider ACTH deficiency. Get the following test and revert back . Complete Hemogram , Serum TSH , FBS, PPBS , LFT , Serum Lipase , Ultrasound Abdomen Pelvis , CRP. Hope this information is useful to you. Any clarification feel free to ask.