It's great that you're walking and watching what you eat. The trick to losing weight is to burn more calories than you consume. Even though it sounds like you've increased the output, it might not be enough compared to the input. Ramp up your exercise by walking longer and/or at a faster pace and/or carrying weights (a backpack with a 5-pound bag of sand, ankle weights or carry small dumbbells). Really analyze your diet and make sure that you're eating healthful foods in a wide variety and your portion sizes are what they should be, not what fast food places tells us they should be. Drink lots of water, not pop. Good luck.
Walking isn't really the best way to go about losing weight.. I'd suggest, if you want to see results faster, you switch things up and start jogging instead. A doctor told me once that it's been said that unless you're sweating and your heart's racing, it doesn't count as exercise. Not saying that that's necessarily true, it's just a thought.