How can i lose 30 pounds by this thanksgiving?

Hi everybody, im 5'3 and 12 years old i weigh i hate saying this but 141 pounds id really like some encouragement on losing weight. I dont look fat or skinny and im not made fun of!!!=) When i say this im saying the truth most of its baby fat not having a baby but you no what i mean, and some of it my doctor says its also from my asthma mediations i had asthma since i was 4 years old, it makes me cry to look at the pictures i saw of myself when i was little like wen i could walk; around ages 1 and a half to when i started using medication for asthma. I was sooo skinny i couldnt believe my weight now. After a while i ate alot of junk food which could be partly the problem also i am indian which mean i eat alot of rice(white) and stuff oh im, south indian just to let you know i try to eat only one cup of rice each day for dinner, make lunch 3 times a week when i go to school regular lunch P B and J sandwhich usually or tuna loveeee tuna with onions, and some water and a snakc like raw fruit and when i come home from school i eat and apple as a snack and then i have 3 gles of milk each day one in the morning and atleast 6 to 8 gles of water each day. also have gym 2 days of the week. I walk on the treadmill for a half an hour each day, should i do more??? ill usually eat some cereal (speacia k) or (kashi) in the morning, or ill have one waffle, or i will either have eggs, love eggs!!!, oh and mabe a bagel sometimes with a bit cream cheese?? anyays my brothers make fun of e and say im fat which makes me kind of sad to know that there old and mature hic makes ithard to believe tey would do that ones 19 in college the other one is 23 in med school!!!!If you guys can tell me a few tricks to keep me motivated and some tips and how to lose 30 or more pounds by this thanksgiving that would be just super!!!!!!!ohh and im also gonna do softball and basketball this year so ya!!!!!!! o and i didnt have my period yet my mom sas ill probably lose some weight from that, the doctor said ill get it this year smetime probably. well thanks a bunch and plesse people out there i really need help my cuzins re all skinny and my brothers are both fit in shape strong and go to the gym run ALOT!!!!so there both fit andi would probably hae a semi flat belly if i lose my baby fat!!!One more thing im not going to get liposuction or and any surgery and im not taking any pills aiight ok guys thank youuu so much for the people who tok the time to read this and answer!!!!!!!!