I did WW which was good, but then stopped tracking my foods and piled it back on. Now I use My Fitness Pal which is helping me to be more aware of the junk I am or am not eating and how to best balance out exercise. I have also very recently discovered I love sushi, which is great for me right now because I find to be extremely filling and low in fat, carbs and calories.
Dog walking and general walking is good to have as a routine in a healthy life, but I think if you actually want to shift stones and pounds you need to focus on more burnign calories through aerobic cardio workouts and reducing intake of things such as calories, fats, carbs and so on.
However if you have a medical condition, then wouldn't you be best off going to your local GP or nurse and getting a proper diet plan off them?