First of all, I don't think it is advisable for you to eat an apple a day. You are a student, and you are developing. When you need nutrition, how uneconomical it is to lose weight and affect your height and chest! Moreover, our bodies have the function of self-regulation. It found that if you eat less and think that you are short of food, you will automatically lower your metabolism. This is how our ancestors survived in primitive society. It is better to eat normally in the morning, be full at 7 o'clock at noon, and only eat some vegetables or cereal at night to tell your body that there is food and there is no need to reduce your metabolism. It's easier to stick to it. Otherwise, you put up with losing a little weight for a week, then eat normally and rebound next week. What a bargain!
Doing yoga is a good way to lengthen your muscles. I suggest sticking to it!
If you still have time, do some aerobic exercise. Not only does it consume fat, but it can also improve metabolism for a day or two. The calories consumed are considerable ~ two or three times a week is enough.
4, about not losing weight. Well, what we want is figure, not weight. No one will ask how much you weigh when you meet. No matter how light the weight is, it is useless to keep the waist and leg circumference unchanged. So buy a meter ruler to measure your weight loss effect! Moreover, it is possible not to lose weight for a week. Many people have calculated that at the initial stage of weight loss, the weight will not be reduced, and it may increase. Often the weight remains the same for many days, and suddenly drops a lot in a day or two. The mechanism is unknown.
Gain weight like a mountain, lose weight like reeling. Give your body time, and gradually reduce it to health without rebounding.