Ok, first of all, you need to have unprotected, VAGINAL sex to get pregnant because that's your reporductive system and the anus is part of your digestive system. The two aren't connected, so there's no way semen deposited in your anal canal will somehow reach your UTERUS, which is part of your reproductive system.
secondly, since you got off your period 5-6 days ago, chances are your fertile days are about a week away, but this completely depends on your usual menstrual cycle length.
I would really suggest reading up on the human anatomy, a woman;s menstrual cycle, reproduction and birth control.
Are you in your teens? If yes, it is especially very important to arm yourself with knowledge about pregnancy, birth control etc. to stave off an unwanted pregnancy and avoid contracting nasty STDs.
You can start here:
http://www.innerbody.com/
https://en.wikipedia.org/wiki/Menstrual_cycle