I understand that desire to lose weight, particularly when it's weight that you've lost before, but the first thing to say about your situation is that you are a perfectly healthy weight for your height. So irrespective of how you may see yourself, it is highly unlikely that you need to lose weight for any sort of health reasons. Your weight is perfectly fine.
That said, most people will empathise with the desire to lose weight, and if you want to do that there's broadly nothing wrong with it. However, you do have to do it right. Losing weight from being sick is something that happens from time to time when you are ill, but it is not a healthy way to lose weight. Being ill has given you a glimpse into what you look like when you're 48kg, but it's also given you no barometer at all for what it takes to get to that weight in a healthy way. So if you do want to lose weight, you need to understand the process by which you can do it in a way that maintains your health. And that way is a combination of exercise and diet, but mostly diet. And no, I don't mean "a diet", I mean eating healthier and in moderation. That combined with exercise may result in you losing weight, but it's a process, and maintaining that requires you to take a broader view of your health as well as just the amount that you weigh. You're focused on how you physically look, which is understandable because that is the focus for so many people, but having a healthier lifestyle has so many more benefits than that. If you can, I would look to improve your lifestyle by considering the things you eat and the exercise that you do. Find healthier foods you enjoy, and find exercise that you enjoy rather than doing it for the sake of it. Changing your lifestyle in that way is much more sustainable and positive, and will bring more benefits to you as well as losing weight.