I had unprotected anal sex a week before my missed period. is there a chance that im pregnant?

Anal sex: You simply CAN NOT become pregnant from anal sex. You have to have Vaginal sex to get pregnant.

Unlikely: Unless the ejaculate was outside the anus its unlikely that this could have fertilized. Even outside anus is unlikely but to be safe.....have a pregnancy test....(you can use an OTC kit in another week or two. Hope this helps Good luck