Your wt at this age and at this ht should be between 56 to 72 kg,so it is definitely less.
To increase wt medicines are not of much use.
take nourishing diet containing high protein diet like more pulses,cereals and milk with high fat.
take dry fruits,dates,gud, and fresh fruits like banana,apples,chikus.
add eggs and omlets in your breakfast.
you can take multivitamis and minerals suppliments.
If you have less appetite you can take ciplactin
after consultation with your doctor,ciplactin is non hormonal
and stimulates your appetite.