My metabolism went down at 17 years old. I gained 15 pounds in one month...course I was so skinny when you look at me today youd never know it was gained weight lol. I hated my weight back then though, everyone swore I was anorexic, but I just couldnt gain weight. Not only that but I lived with an abusive mom, stress makes you keep weight off or gain it depending on who you are.