Ok I have said this like a million times, but...
Anal sex itself does not get you pregnant, your rectum is not connected to your re-productive system.
The only way this can lead to pregnancy is if some sperm "dripped" down past your vagina.
However you should always wear a condom for anal sex as it is such a high risk of infection.
End result anal sex itself does not lead to pregnancy.
The original poster, you maybe did get pregnant but given the fact that pregnancy is caused by sperm entering the reproductive system and you had his penis in and around your area then it's no suprise really is it.
Any way sperm can get into a vagina they will.
Tha also means you are only a technical virgin, not a "virgin" virgin, ie done everything but actual intercourse.