My mother is in a similar position.
Do you get enough calories in a day? She has GI problems and eating enough to satisfy her basic energy needs has been a challenge (if she doesn't watch it, she will only get 500-600 calories a day), but she has made great strides the last week.
Once we made sure she was eating enough, the diet started working very well. It's been a bit of a puzzle and we are figuring it out piece by piece (food sensitivities, etc), but each step seems to be cumulative, and the progress is so nice to watch. Still a ways to go, but at least we finally found something that helps her. She's on the forum, maybe she will post here.
Good luck to you. Some people think that folks like you and my mother are "lucky" because you don't have extra weight to lose, but they don't realize the other kinds of challenges that might face you.