You are such a sweet husband to be writing in worried about your wife!! Its nice to see men so involved in this whole process. First off, yes going off of any hormonal birth control can mess up your cycles. When I came off of Depo Provera, my cycles were all over the map for 2 or 3 months at least. And if you have been using protection, it is unlikely she is pregnant, providing you are using it properly.
If she is a week late,there is a small possibility she is pregnant. Regardless, taking a home pregnancy test right now will at least serve to put your mind at ease, the wondering and worrying are always the worst. If in fact she is pregnant, please don't worry too much. Lots of women get pregnant right after coming off of birth control, and all turns out just fine. Her Dr. can give you all the info to put your mind at ease.
Good luck to you!!