The purpose of this study is to learn if women gain weight using progestin-only methods of contraception and if so, how much. The investigators will look at users of two progestin-only methods: the levonorgestrel-containing intrauterine contraceptive (LNG-IUC) and the etonorgestrel (ENG) subdermal implant, and compare these users' weight change to that of users of a non-hormonal method, the copper intrauterine device.