I think people gain weight when they quit the oral habit that vaping replaces. Maybe it's the nicotine though. Anyway, I had the same problem when I was young. People think it is hard to lose weight, but gaining weight can be just as much trouble. I was painfully thin forever. Age will handle this problem for you. Just wait, when you turn 26 your metabolism will slow down and you will gain weight. It happens again in your 30's and you will gain still more weight. It just keeps slowing down from there as you get older and older. It's best if you are lifting weights during these periods so the extra weight turns into muscle instead of fat. When I turned 26 everyone accused me of taking steroids since I gained so much muscle mass, but I really was just doing the same things I had for years.....