The best 2 ways to gain weight are to lift heavier and to consume more protein and carbs. I am not a dietitian I am going off of what worked best for me. I went from 150 my junior year of high school to 170 in one off season and that is the age most of you are at. I changed how I lifted and what I ate. In the weight room I would always lift for reps and didn’t care much about form or lifting heavy. I was lifting to cut down and get lean and I was. But once I started lifting heavier, 3-5 reps 5-8 sets I started to put on mass. That’s what helped me gain weight. Now you have to be consistent. That’s the problem. A lot of guys lift for a week, don’t see anything, then quit. It doesn’t work like that. Consistency and discipline is how you put on weight. Now for food, that’s such a huge part of the process. I would drink a gallon of water a day. No excuses about that. That is an absolute must. Then I would eat 5 meals a day. Which can be tough with school but that’s where discipline comes in. I would also have protein shakes in between meals. Now your meals should be high in carbs and high in protein. Please don’t use fast food as one of your meals. Meal prep the night before. It makes it go so much easier. Chicken, pasta, rice, eggs, meats etc. those are the best things for you if you want to gain weight. Lift heavier with a focus on good form, eat more calories and be disciplined. That’s how you gain more weight.