Dd17 thinking of starting injection as her form of birth control as well as condoms. However, her periods are quite irregular. She has only been keeping track of them since last summer when she had a pregnancy scare but they are all over the place. She's currently two weeks late and we've done a test and its negative but she was a week late last time as well. In view of this, would injections be suitable? Would she be able to start without a period?