First of all, congratualations on losing that much weight. 20 kg in 4 months sounds like fairly rapid weight loss, and that pace may not be sustainable. A lot of people see a plateau at some point when losing weight, after which they can continue to lose weight but more slowly. However, if you still have fat you want to lose there are ways to keep it coming off.
The right thing to do when weight loss slows down depends on a lot of things. How old are you? What are your fitness goals beside weight loss? What changes to diet and activity did you make to lose weight in the first place? How much more weight do you need to lose to reach your target weight? How well has your lean body mass held up during your initial weight loss?
One reason many people see some weight loss but hit a plateau is that they have lost lean bodym *** (mostly muscle) while losing the weight. This especially can happen if you caloric intake was very restricted. Muscle burns a lot of calories per pound, so losing it reduces the rate at which your body burns fat. This means that if you have lost some muscle mass in the past few months, you should probably look at some strength training to replace it. This is good in many ways, not least in that it also improves your health and appearance in ways that make the most of your recent weight loss.
If you can provide more information we can provide more specific advice.