Welcome to Beyond Blue forums. I am very pleased you've found your way here. You sound very upset for a 13 year old. By the way, you are not bothering us at all by writing here. That's what the forums are for. So good on you for being able to write about yourself so clearly.
The media and social media is so full of images of the 'perfect' body. It bears little to reality. There is no 'perfect' body. Everyone comes in different shapes and sizes. But at the age of 13, this is magnified for you because you are starting to become a teenager. So everything matters, especially size.
It doesn't sound like you are able to talk to your mum or dad about how you are feeling. Am I right? Do you have a grandma or aunt you can talk to? It is really important that you do. At 13, you are changing. The story you tell yourself about how ugly and fat you think you are, is just that a story. Possibly something you've heard someone else say to tell you. It does not mean that it is true.
My thoughts are it is very important that you talk with someone about how you are feeling. Whether you go to a school counsellor or contact one of the organisations for kids, e.g. -
eHeadspace 1800 650 890
Kids Helpline 1800 551 800
BB support service 1300 224 636
I'm not a young person, nor do I have children. So I am hoping there are others on the forum who can help you out here.
My thoughts are with you at this difficult stage of life.
Look forward to hearing from you.