Please help me I'm suicidal over my weight.

I am only 15 years old, female with a rare medical problem. I am 25 stones 6 lbs, I'm in year 11 and my prom is coming on June 28th 2012. I bought my prom dress the other week and it does not fit I need to lose weight from my back, bust, waist and tummy. I can not under any circumstances return the dress, I cannot get a new one because we don't have a lot of money and I have the biggest size (UK 28). Please help me I have tried everything. I am sick I can't do anything to help me lose weight. I am close to suicide and I am very serious please help me please just give me some advice please on what I can do to lose weight to fit into this dress I can't take being fat anymore I HAVE NO LIFE PLEASE HELP ME I NEED ADVICE!!!!

ADDED BIT: thanks for the advice everyone but I need to mention one more thing.
I am not able to be a vegetarian because my body lacks protien and iron (I am anemic also). Also please if you could recommend some normal healthy everyday meals that would help. P.S thanks for the bit about memorizing me in my prom dress that is a good tip.

First things first.. Suicide.. BAD IDEA! I have come close and I realized that I was being stupid (not saying you're being stupid). Enjoy life and love your body. I dont really know much about losing weight because i'm REALLY REALLY SKINEY! I don't really like it either..
But anyways if I were you I would get active. Go with your friends and take a nice long walk. Find a sport or activity that you actually ENJOY doing. Many people go to the gym and work out but a lot of them don't like it and they stop going because to them it's more of a chore than something they enjoy doing.
Also, I think that fish/salmon is a very good meat for you to eat while trying to diet.
You have your motivation, which is your prom. So just keep your eye on the prize and don't take your eye off of it...
P.S erase suicide from your mind. If you think that you don't have a reason to live , then just do it for me. I would hate for anybody to kill them self over there weight!

Easiest way I've found to lose weight is to eat very healthy. Like, I'm a vegetarian now, before I became one I was over 250 pounds. I went through the same thing, well except for the dress problem. I told myself that I would lose the weight. Basically I exercised every single day, and I stayed away from all junk food. I ate healthy and exercised. That's the secret to losing weight. You have to change your lifestyle. Diets work, however, they are only temporary. I hope this helps you.

The first thing you should do is changing your food pattern.

Drink only water, no fruit juices or lemonades they contain loads of sugar and no light lemonades, they may crate a feeling of hunger.
Also you should pass on food that consists mainly out of carbohydrates or fat.
Your diet should mainly consist out of vegetables, like tomatoes, cucumbers ect. they consist mostly out of water and cellulose so they don't provide a lot of energy and you can eat them until you are full.
To keep you healthy you should add food that consists mostly out of protein, like chicken meat, you can also get protein powder, you mix with water, not milk, it makes you full quite fast while providing important amino-acids without carrying a lot of energy.
To find out which food hits these requirements you can look them up in the Internet or take a look at the back of the package.
With this diet your body will need more energy that he gets out of the food and so he will start to use bodyfat to fill this gap => You lose weight.

Next step is to increase your need of energy. For the beginning I recommend that you go swimming, it doesn't put a lot of strain to you bones and joints because the water carries you. When you have lost some weight you can start training you muscles with weights. A muscle keeps needing some energy even if it isn't used at the moment, and it burns a increased amount of energy up to 12 hours after exercise. Later on you can go cycling for example.

To keep you motivation up you should create a picture in your mind of you with the weight you are aiming at, wearing you new prom dress. Memorize this imagine well and recall it everytime your motivation drops. This picture will help you keep going. This method is used by US Navy Seals to get through Hell Week, so it definitely works well.

I hope you physical condition allows you to take these steps, if not, inform us and we will find something else to help you lose fat.

Everyone is beautiful in there own way - suicide is a permanent solution to a temporary problem.
Breakfast - weetabix & banana
Lunch - jacket potatoe - tuna - beans.
Tea - chicken / fish / steak - but cooked healthy and vary it look on the internet for diet ideas.
Also exercise is vital - go for walks to start off twice a day for 2 weeks then pick up the speed till eventually you can do a slow jog. Set your self targets when running like " I will get to that lamppost then walk then run again at the next one"
Things CAN workout think positive you can do anything you set your mind too.