Hi Doctor! I'm 26 Years Old, I Was Wondering What

Hi Doctor! I'm 26 years old, I was wondering what is a normal weight for my age? Also since I'm small and petite it's really hard for me to gain weight since I have a fast metabolism.is it going to be hard for me to gain weight when I try to get pregnant? I want to have kids in less than 5 years.is it going to be hard for me to put baby weight on? I hope fast metabolism doesnt cause infertility :(