I was really irregular when I first started my BCP. The doctor told me to wait until I got my period and then start on the Sunday following the START of my period. After weeks of waiting and no period, I called my doctor and the nurse told me to just start it on Sunday even if I dont get my period. She said it was perfectly okay. At the end of my first pack, I got my period. It should be fine. But like always, you should probably call your doc to make sure this is okay.