As per standard at this age and ht you should have weight between 49 to 66 kg.and you.have got wt 48,49, you are not under wt. but minimum of normal so you may require few more kg wt.
You take more protein and good amount of fat and carbohydrate
so that calorie intake will be more and thus positive calorie balance will bring your wt raised.
Take more dry fruits,bulky fresh fruits and eggs.Use of more cereals and pulses also will put weight.