Your ideal weight is between 75-77kgs as per your height. You can increase your weight by having excess of calories but that's not ideal as it is unhealthy. So the ideal way to go about it is by exercising and building muscle weight . These following steps may help: - Don't skip meals, you may not feel like eating but in such conditions you should have the reduced amount in frequent intervals(i.e. 3 square meals broken down to 5 or 6 as you can tolerate) and slowly increase as you get better. - Reduce/ Avoid spicy,fried, fatty, junk and oily food - Exercise regularly - Increase daily intake of water to 3 liters - Avoid/Stop smoking and drinking - Reduce stress through methods such as yoga/meditation.