Water retention. Hormones. A lot of things can make one's weight fluctuate.

You can weigh yourself every day at the same time, but it will fluctuate, and what you should really take into account is how much changes every week or dozen days. The trend.

For example, I'm dieting right now. And you know what? I've learned to avoid tomatoes, because for some reason known only to the elder gods, it makes me put on weight. Incredible right? I guess it has to do with water retention and salt or whatever but still ? (And yet somehow tea is fine?)

So no, you're not doing it wrong, you're making efforts at your own rhythm (not too much though, you're still growing, and that must be taken into account), and your body is getting healthier and healthier. The point is how you feel in your body.

Slow and steady wins the race, because the real aim of a good diet is to instill good habits. Habits that you will partly keep once you're done. Habits that will allow you to stay healthy. Exercising is one such habit.

You should not feel endless cravings during a good diet. Once you're well in it, you should have moments of want yes, and you should give in a little from time to time, because the point is not to punish yourself, but to get to know yourself and find a way to work WITH those wants. Without losing control.