I have very poor digestive system.my stomach couldn't digest food properly. my age 23 and weight is 45 kg. ?

You might try...: 1st,see a Doctor.It sounds like you have a malabsorbtion syndrome which could be parasites, infections,dietary intolerances,or inflammatory diseases.You need stool studies, and blood work.In the mean time I suggest an elimination diet.Eliminating all dairy&all gluten, then reintroduce if you are feeling better. this leaves potatoes, rice, corn, meat, fruits, and vegetables.Try to cook all u eat.