Dear Katie, I'm sorry to hear that your doctor produced a mistake and put you on Depo injections. You say that you are still finding injections? These injections are created from progestin, a synthetic form of progesterone which is used mainly as a method of birth control for women who cannot use any other form of birth control. Among the drug’s side effects is weight gain. A single injection lasts for three months. So if you are still getting these injections, please, please, tell your doctor that you don’t want to receive them any longer. The effects of the drug will remain in your body for three months, so during these three months, it may be difficult to lose the added weight which you gained, no matter what you do. You will find other far more gentler ways to regulate your periods and menses, especially at your tender formative age. Here are some with the negative reasons for not using Depo-Provera: it can cause decreased bone density which can lead to osteoporosis, depression, ...