I agree--when you've visited the 3FC forums for awhile, you see all kinds of stories from folks who can't lose, even though they "do not eat that much." But unless you are tracking it somehow, you can't really know. It doesn't have to be FitDay, although that's really easy to use--you could do it with a calorie-counter book or some other Web site.
Try tracking for a week, NOT to change it, but just to see what's up. Write down everything you eat during the day and how much (ounces, cups, tablespoons, etc). Don't figure calories yet. And then in the evening, do the calorie calculations and add it up. Or, if you're using FitDay, it will keep track for you and you won't have to do any calculations.
It's good to walk!
You may want to add some other exercise as well once you've been doing that for awhile.
Jay