Why am I never hungry

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Hi, I'm here because I haven't been hungry in the past few days. I don't know what type of information is needed but I'm a 13 year old girl, (14 next year) 152 cm (about 5 ft) and weigh about 39 kg (about 86 pounds). 3 days ago, I went out to eat late at night, I had a cup of milkshake and came home around 12.30 am. (I never really do this.The last time I did it was about a year ago and this never happened) The next 3 days, I never felt hungry and always felt bloated.My waist used to be about 24 cm but after that night it became 25.5 cm. I know it's only 1.5 cm difference  but it has always been constant at 24 cm only after that night. I not even sure if that was the cause. I have never changed my eating habits before. For breakfast, I usually have a bowl of cereal, I eat 3/4 plate of food for lunch and dinner, and some snacks in the late afternoon. I still try to eat the same portion everyday. I have read other websites and it said that it may be due to stress,anxiety or depression, but I'm quite sure that that's the case as school just ended for me. Also, I don't have any problems with any thing. This has never happened to me before and I honestly appreciate any help I could get from this. Thank you!