Why do i feel like this? (GIRLS ONLY)?

i know you might say im young to be asking this but these days it seems more important than ever. I feel SOOO fat, my arms wobble when i jump my thighs are thunder and when i sit down in school its embaring when i wear a skirt or shorts cuz cellulite forms, my stomach is pretty flat but has a weird fat lump near the bottom, everyone says im sooo skinny. but i dont belive them. im 13, 109 lbs, 5"1. i also feel WAY short everyone i feel im looking up at i get made fun of alot about this. i have alot of friends who love me and i love them. but i always feel my appearence is ugly and i hate my body. Most my friends have perfect B size , and i dont have any. i wear a size 34 A but my s dont even close to fill a 30 A. i hate them im fat with no it feels. I hav a NuBra if u know what that is, the thing that pushes your s together to make clevage, ya well i use that sometimes and it works but i have to pull the cup back SOOOO far, to even get a tiny clevage. i know im not the most confident , life loving , perfect person. and i want that to change. please help. if theres anything you have to say about this? advice? links maybe? exercise routines? diets? creams? gels? stories? anything!!!!! please. thank you. and DONT tell me what size bra you are? i dont care if you hate your . i would rather have big than nothing, its SOO embaring. please? and dont say anything stupid or rude, thank you.