im on the injection

hey guys does anyone know how long the injection stays in your system? i know it is meant to work for 3 months, but for me i start bleeding at 2 and a half. but me and my boyfriend are planning on having a baby but im on the injection! we are planning on one once this injection is over and done with... i had it at the end of september so i have a month and half left but not sure when will be the best time to get my hopes up about becoming pregnant...