For almost everyone, the desire to have sex is a completely natural feeling. It can be over ridden by outside influences or by the medication or other things that we take into our body.
It is always essential to rule out any biophysical causes. Your wife MUST consult her physician and go through whatever testing is necessary to rule that out. That is #1.
If you have done that, there are a couple other things I may suggest. Many people, especially heterosexuals, define sex as intercourse. Learn to enjoy any and all of the various elements of sexual interaction. Especially if your wife is uncomfortable with intercourse. I am not suggesting that it shouldn't be part of your marriage, but rather that emphasis on other things right now may help relieve some of the stress and inherent resentment that can come from being avoided sexually.
Secondly, have a lot of fun talks with your wife, preferably out of the bed where she can feel safe, about her fantasies. See if you can determine what turns her on. It is important for her to feel safe with you, because some of these thoughts may scare her and she may even be trying to repress them.
I know that we had a very similar problem. Although in my case it was me, not my wife, who lost interest in sex. We discussed our fantasies, indulged in them, and BANG our sex life went from once or twice a week to 8 or 9 times a week almost immediately. ANd that is where we are now. Will it last? Who knows. But at least I know how we got to where we are, and we'll just do it again.
Remember, nothing is out of bounds when it comes to fantasies. Acting out, of course, is a different matter. Let her know that you just want her to free her mind and share her mental pictures with you. It will help you know her better. If she wants to hear about your fantasies, tell them to her as well.
Perhaps you could even role play your fantasies. You can really enjoy each other so much if you can get back in track, and you will find that your "issues" will have served to bring you ever closer to each other.
The most tempting thing would be to give up. I did that with my first wife, which is why I now call her my first wife. The ultimate deterioration can be almost beyond resolution. I am sure neither of you want that.
divorced in 2003 Married in 12/2005 born 1948 wife born 1958 divorced in 2001