As per age and height weight should be near atleast 55kg.just check is any health issues goig on? or poor digetion or low kal intakes, try to find out reson,if possible plz talk with best dietician personally so the will suggest proper diet + exercise and do /donts. personaly i treated so many clients like you, if interested ...can tk my appointment through practo.
Next Steps
now day do very less exercise and more carbohydrates, more protein diet along good amount of fats/ sweet. may it will helpful & u can eat also...banana, aloo, paneer, ghee, chana,sweet potato, soaked peanut, peanut butter etc.
Health Tips
to know more in detail please consult with nutritionist and dietician. thanks for questioning.