Before I start, I'd just like to say that I think a lot. I'm going to throw out a bunch of different thoughts. Please don't assume that I'm making any assumptions about you and your wife or your relationship. I'm just going to say a lot of different things because maybe there is something there that does pertain to you.
First off, there is nothing wrong with craving physical intimacy. It's natural and everyone desires it. However, my question to you is are you seeking true intimacy or affirmation? I only ask this because you said, "My confidence is at rock bottom and the lack of sex is eating me up inside." When a person mentions confidence, it's more about self-assurance. So it sounds like what you want is not relational. Intimacy is relational.
When we get an illeostomy, it is something that changes our body image and affects our self-esteem. The typical response is to wonder if others will still find us desirable or attractive. Many people's biggest concern when wearing an ostomy is dealing with issues of intimacy....that and smell....(Devrom inner body deodorant works wonders for that, by the way). No matter who you're with, the only person that can help you with your self-esteem is you.
From personal experience, I can tell you that I have made sex awkward for my partner because of my insecurities. Those insecurities came out in different behaviors: The lights had to be out; I couldn't be on top because then he could see me; if the pouch was making sounds I was out of the moment...I was self-conscious during the act and so my behaviors reflected that. The sex wasn't about my partner, but about how I felt about having sex with him. It is possible that your approach to your wife is projecting your insecurities, and you don't realize it. So in other words, you may not be initiating intimacy to be close to her, but initiating sex to build your confidence and self-esteem. She may be picking up on that. (I'm not there, so I don't know. Just throwing out some thoughts).
Obviously, I don't know your relationship with your spouse to really comment. However, as a woman I can tell you this. We like sex too. I know people like to say that men and women are different in that area, but I really don't think so. We're just different in the way that we receive it. As a woman, it is a real turn off when men are trying to initiate sex and not intimacy. Intimacy is not sex. Intimacy can lead up to sex, but sex does not lead up to intimacy. Look at how many people have one night stands and never think of that person again. Sex does not create emotional attachment, but intimacy does. If she is not sleeping with you, she might not feel very close to you.
Whatever is going on with her, in my opinion, has nothing to do with sex. Don't ask her what she's feeling when you're confronting her about sex. You said that you've tried to talk to her about the issue of sex, but she gives you no reason other than she doesn't feel like it. Have you tried to understand what is going on with her outside of sex being the main focus? If you're only encouraging her to talk, or justify why she isn't sleeping with you, you're going to make her shut down more.
Work on rebuilding intimacy with your wife. Touch her in non-sexual ways and without expectations. Flirt with her and court her. Opening yourself up to her will encourage her to open up to you. Ask her about her day and tell her about yours. Try doing things together that she likes to do. Remind her daily about how much you appreciate and love her. Basically, do all of the things you did to get her to become your wife.
Now don't get me wrong. There could be things going on with your spouse, emotionally, that she is trying to sort through. Those issues could be related to your condition or the fact that you wear an ostomy. Wearing an ostomy doesn't just affect the wearer, but the intimate partner as well. The issue that you guys have may be about your ostomy. But also keep in mind, that it may not be about your ostomy at all. Your problem may just be a relational issue. Sometimes people with ostomies or people with chronic conditions will assume that an issue is related to their condition when it's not. So much of our lives revolve around our condition that we naturally make associations to it. We have to regularly remind ourselves that we are not ostomates. We are people that wear ostomies. So we manage the condition, we don't let the condition manage us.