I would advise you to keep a food diary. Fitday.com is free and lets you track activities, weight, food, body measurements, etc.
Also, to get more answers it might help to translate the kgs and cms and Aussie sizes into lbs, feet and inches, etc. It seems most of the active posters on the board are American and we still don't use the metric system here.
I'll do it for you this time:
69kg = 152lbs
163cm = 5'4"
Aussie size 12/14 = US size 8/10
Aussie size 8/10 = US size 4/6
Mmm... can't believe people don't know the conversions between kg/lbs and feet/cm... im from Aus but I know my weight in stones/kg/lbs!
Anyway.. OP.
If you ENJOY walking/running by no means stop it! I know PLENTY of people who have lost HUNDREDS of pounds just by walking. I dont think you need to do 90 minutes though, that seems a bit excessive. Maybe doing 60 minutes of fast walking would be sufficient?
Also. You will see much more results with proper nutrition. You dont need to count calories, just eat when your hungry and stop when you are content. Easy to say but this is actually very hard! Make sure you are getting lots of fruits and vegetables (2 fruits, 5 veg per day), good fats (from avocados, olive oil, nuts/seeds), lean proteins (lean red & white meat, natural peanut butter, nuts, eggs, dairy), complex and fibrous carbs (always go for wholegrain instead of white) and make sure you are drinking plenty of water!
Example of a day (approx 1500 calories)
Breakfast
1/2 Cup Oats made with water (porridge)
1 Banana chopped up in porridge with cinnamon
Lunch
Wholegrain Pitta Wrap w/ Roast Chicken Pieces, Lettuce, Light Sour Cream, Sweet Chilli Sauce. Toasted or served fresh with other salad.
Dinner
200g Grilled Chicken Breast with 1/2 Bag Mixed Lettuce, and other salad vegetables such as cucumber, tomato, carrot, celery. Use a low fat mayonaisse or a low fat dressing on top.
Snacks
Apple
Banana
Tub Low Fat Yoghurt
Handful of Almonds, Macadamias or any other raw unsalted nut