Welcome to HealthcareMagic
According to your height and weight for your age , Body Mass Index
(BMI) is 16.2 which is much below the normal ( 18.5-24.9 ).Your ideal body weight should between 52kg-57kg.Weight gain is a slow process, since your involved in field work , the energy expenditure is more and your intake of food should also be more in protein and energy gives helps to build muscles abd stamina.Your diet should be rich in protein with whole legumes, pulses, milk products, lean meats, egg ( daily ), soy milk ( high protein , low fat ). Take small frequent meals rather than three large meals.Snack healthy between meals with nuts - a handful, fruit milkshakes, yogurt, flavoured soy milk, cheese sandwiches, paneer or tofu tikka / cutlets, nuts / dry fruit milkshakes. Avoid taking junk foods like oily fried foods, carbonated drinks, highly saturated sweets , too much of coffee which all will suppress your hungry.
Drink plenty of liquids to stay hydrated.Take some protein supplements
with milk instead of other beverages which will add the needed protein.