I have unprotected sex on sept. 15. I took plan b and I started my period 2 days after the sex and it lasted for about a week. Which is normal for me. Since then I’ve had 2 more periods all lasting the normal 6-7 days. I’ve noticed my back has been hurting a little and I’ve been more hungry lately. Maybe it’s just from my period, but is there any odd chance that i could still be preg even after 3 full periods?