All of the changes you made are REALLY good, healthy lifestyle changes, so please don't lose sight of that!
However, when it comes to losing weight, you have to burn more than you eat, bottom line. If you don't know how many calories you should be eating to enable weight loss, and if you're not tracking them, it's hard to say whether or not you should have been losing weight.
Taking the excellent changes you've already made, now add a little calorie analysis to your program. It doesn't have to be drastic or be complicated. If I were you, I'd continue to eat and walk as you normally do for a week, and track everything you eat in www.fitday.com
. This will give you a great picture -- complete with pie charts! -- of what your current intake is. Then you can look at how your calories are distributed, and if you need to cut back in a certain area, or just a little overall. If you want a ballpark estimate of how many calories you might shoot for for safe, gradual weight loss, check out http://www.jimkaras.com/loss_math01.cfm
The other thing that can help burn calories throughout the day is weight training. Adding muscle while you lose fat will increase your resting metabolism AND make you slimmer overall, even if your weight doesn't change that much.
Good luck, and keep plugging away. I know you're frustrated right now, but you've made such a great start to lasting health, you just need to go to the next level now.