You need to provide more information. If the two of you weren't living together before marriage, then maybe the change in routine may have something to do with it. Living with someone after living by yourself is a big deal, and some people may take longer than others to adjust to the change.

Also, it could go to the length of time that you've been married. Generally, the frequency of sex has been known to decline as time goes on. It could also be that maybe you have to try something new. She could be bored with the same sexual routine.

Have you tried asking her what the problem is? Communication can take the guesswork out of a lot of things.