Why did i gain weight so suddenly?

Im 13, i stopped growing in height in the summer of last year but i didnt really notice or care. I used to eat anything i wanted and a lot of food and still look great but in december i started gaining weight and my stomach started being bloated and big all the time even tho i didnt change nothing in my diet, i gained 5 kgs without doing anything and ive grown to hate my body, is there any explanation for this? I struggle not to eat everything i wouldve ate normally because now im gaining weight from food and its not something usual for me