Hi,
Sorry to hear about your lack of success. 4km is great, though!! The scale may not see the difference but your overall health is still getting much better.
As far as weight loss goes, you don't burn a lot of calories walking, so it depends on how much running is actually involved. When I run, I run for 1km straight, but that's probably only a hundred or so calories, which isn't much. If your total daily caloric deficit compared to before walking is only a 100 or 200 calories, it's not enough for your weight to change. Your body really wants to maintain it's current weight, so you probably need to eat less or do a lot more exercise to get over the hump where your body actually realizes that it is going to lose weight.
Everyone hates doing this, but record your daily calories for a week straight. Average it out and really get an idea of how much food you are eating. Then, take out 500 calories (or even a 1000, depending on where you are right now) and keep up the walking / running and you will start to see a change. My average calories is about 3200 / day. But, I have to go to 2000 or less to actually lose any weight at a weekly pace. At a monthly pace, it's about 2500 calories, but it's so easy to go from 2500 back up to 3000 without thinking about it. So, if I am for 2000 and slip a bit, I'm not going to slip all the way back up to 3000.
