Fat Hideous Teenager?

Hi I'm 17 yrs old and once upon a time I was really skinny. Now I'm an ugly fat ***** who weighs 142 pounds at 5'4 ! All the fat has accumulated to my belly and arms never to my thighs which I wouldn't mind as much. I hate this. How can I get beautiful toned arms and a small waist + flat belly by the end of this month !