Hope, It sounds to me like it is mostly the guilt. Doesn't hurt to get hormone levels checked, but I am guessing it is mostly psychological/emotional. I am very thin (size 2) and my drive has only increased as I've lost weight because I've felt sexier and sexier with the weight loss. The ironic thing for me is that just before the bomb I was feeling better about myself than I had in my whole life... now have had to struggle my way back up in my self esteem. But, finally accepting my H's A was not about me, but about him has helped.
Anyway, I agree with Pearl's ideas about complimenting her on more specific things about her as a person.
I think the lingerie for Christmas is a great idea, but also get her something that shows you have been paying close attention to things that are important/interesting to her as a person... so it doesn't seem to be only about sex. Like if you've noticed her admire something in a store or mention wanting to take lessons for something, or a day at the spa to pamper herself if she enjoys that, etc.
