You may have added some muscle, which is heavier than the fat you're losing. While it's not easy for women to gain a lot of muscle in a short time, it can account for part of the difference.
There's also fluid fluctuations to take into account. Your lean mass (everything that isn't fat) is made up not only of muscle, but of bone, skin, internal organs, hair, teeth, the contents of your digestive system....and fluid. So if you're retaining more fluid than usual, your body fat percentage will go down, but your weight may not - it can even increase.
Depending upon what your diet was like before, and what it's like now, you may also be storing extra glycogen in your muscles and liver. This is always accompanied by a lot of water, so again, your weight and BF% can be affected.
Doing 'mainly cardio' may not be the best strategy to lose fat. A decent weight training program will build muscle, and boost your metabolism so that you burn more fat. There are a lot of other reasons for doing more weight training, but it would take me forever to explain them, and I'm off to bed soon.
Body fat scales are notoriously misleading, and the figures can be out by a LOT. To determine whether you're actually getting any results, answer these questions:
- Can you SEE any changes in your body size or shape?
- Have your measurements decreased at all?
- Are your clothes any looser?
If all the answers are 'no', you might want to change your exercise routine and/or your meal plan.
