I need to lose 20 pounds before Christmas break ends. I don't care about how unhealthy it is. I'll do it.?

Okay so my height is 5ft. I'm 12. And I weigh 100... This may not seem that much to others. because my appearance is skinnier than most at my school. but honestly the only reason it looks that way, is because all day each day at school and at home. I suck in my stomach. No one notices. And if i didn't then well i'd look absolutely gross.

What i call skinny for a girl is when either their chest is bigger than their stomach. or if they just have like those tiny little thighs that we all can't help but envy.

So when i come back from Christmas break, I don't want to have to do that anymore. It's stupid i realize that. And don't give me any of that "Oh you should just be happy with your body." I'm 12 i have alot of energy.

I have a stair stepper, a treadmill that doesn't work anymore from over usage, and one of those really expensive weight lifting things. So how can i lose 20 pounds before Christmas break? Which is only 2 weeks i think...

Thanks any answers are really really appreciated. Oh and i can't do any of those online ones that make you pay. My credit cards are at the beach house. :'( so ya.... Thanks again!!!!!!