Look - it's very simple. You need to get yourself some sports supplements and start going to the gym. First of all, drink more protein. Do not hurt BCAA amino acids - they are good for you to increase your appetite. Get some creatine - it will increase your body weight in no time at all! Take vitamins. Go to the gym 3-4 times a week at first. It is better to eat 5-6 times a day in small portions. Or better yet 7-8 times a day. For example, Dwayne Jones eats eight times a day. And look at him. So you can't do without the gym and the heavy lifting. You have to eat eight times a day since you can't eat much at once. Make sure you eat before going to bed, right after waking up. Drink plenty of clean drinking water.