Any new diet and exercise regimen you're on will cause rapid weight loss almost immediately. But what you're losing is not fat. You're body is shedding excess water, and you have reduced the volume of food in your body, assuming your weight loss strategy is to put yourself in a calorie deficit.
Scales, especially digital scales, are inaccurate. Even a physical measurement of your body fat is a formulaic process that gives you an estimate of your BMI. Forget the scale, or use it as a guideline for progress, but never for accuracy.
What your body is doing:
Think about how many calories an athlete burns while running a marathon. 2600 calories. It takes 7700 calories burned to shed 1 kg of fat. Marathoners don't even lose half a kg of fat while running a whole race. And that's when applying this conventional wisdom of 1 kg of fat being equal to 7700 calories. Research is now suggesting the caloric value of fat could be double what we previously thought. Yikes!
So... you're likely not losing fat that rapidly. However, don't be discouraged. Here's why.
When dieters choose a calorie deficit diet, and cut their intake by reducing volume, they typically reduce foods that encourage the production of insulin, which is a fat storing hormone. So if you cut out foods such as breads, crisps, chips, candies, fruits, starches, carbs, etc., you are reducing the amount of insulin your pancreas cranks out. The first thing your body is going to do is dump water it no longer needs. The next thing it's going to do is use fat for fuel. The more fat your body seeks for fuel, the more weight you will lose. This can be a rapid process because your body wants to get rid of what it doesn't need to survive. But don't think rapid means a miracle amount of fat will melt off your body. Though 3kg a week isn't unheard of if you are doing this 24/7, be happy with 1-2kg a week. That would be excellent!
My suggestion: forget calories. Don't put your body in a deficit. Don't worry about a surplus. Eat foods that encourage health. Eat foods that are high in healthy fats and protein, eat vegetables that are green and lower in carbs. Your body will burn much cleaner and more efficiently almost immediately. And stay away from fruits! The idea is to burn fat, never to store it.
"Eat fat, get thin" is a good read. Research the slow carb diet, or read up on Tim Ferris's conclusions in his book, "the 4 Hour Body." This is a fun read on body hacking.
And check this out. This is how I lost 70lbs and got to a 550lb squat, and a 550 lbs deadlift (for 7 reps) in less than 6 mos:
Nutrition and lifestyle: https://authoritynutrition.com/how-to-lose-weight-as-fast-as-possible/
Lifted heavy for strength. Volume for muscle growth. You want muscle growth because muscle has a caloric cost. The more you have, the more you burn at rest. Use periodization to alternate between strength and growth. This will make you look good, be functionally strong, and allow you to perform any thing that's ever asked of you.
Lastly, remember that you got this. This is your time! Research, and educate yourself, and just do it. The body will respond immediately. It wants to be told what to do. So tell it - THIS IS WHAT WE ARE DOING! And there's no such thing as failure here. You mess up, so what. Just get back to it as soon as you can. You got this!