my last period was aug 15 and had unprotected sex sept 5 and 6

Yes. When having unprotected sex the possibility of pregnancy is always there. You may not be, but you may well be, there is no way to tell. It only takes one mistake for that to happen. If I were you I would just hope and pray that you will be safe! And if you are, go straight on the pill! Don't risk it, because it's not worth the risk sometimes!