Many health issues can affect a woman’s sexual desire, from diabetes to chronic pain conditions to cancer. Hormonal changes, which can start as early as your 20s, can also be root causes of low sex drive. And lots of different health issues and life circumstances can affect your hormones, as can taking hormonal birth control (i.e., the pill).
All that said, unless your wife has a known health condition that she’s currently managing—or she’s had a very sudden and significant change in her sex drive—don’t assume that her lack of interest in having sex with you means something is medically wrong with her. Start by considering and working through any and all interpersonal, emotional, and relationship issues. Addressing these issues will likely buoy your sex life naturally.
What to do about it: If you’ve talked about all the other reasons on this list and mutually feel great about your relationship (talk to her about this—don’t assume!), then it’s worth her talking to her doctor. Or if your wife does have a known medical issue, talk to each other about how your sex life might be being affected and ways you can work together to keep your sex life healthy. She can also talk to her doctor to see what options are available to support her libido.
Just be sensitive to what she’s going through: If she’s dealing with a significant illness or painful condition, for example, it may not be appropriate to push for more sex at this time. You can bring up your feelings about the importance of sex in your relationship so that she knows and can let you know what she has the capacity for. You can be honest while also being flexible and compassionate.