instead of just running on the tredmill for 20 minutes everyday try changing it up. after a while of doing the same exercise your body gets used to it and you won't loose weight anymore. try doing some days of cardio, yoga, pilates (i know they're girly but they work.) or kickboxing. go play outside (i know it sounds corny but playing tag with a little brother/sister/cousin, hiking through the woods, swimming, riding a bike...etc etc) work in the yard. i know it doesn't seem like exercise but by changing it up you're giving your body something new to do and it still has the same affect as actually working out. or join a gym. do weights some days, treadmill other days, or some of the other gym equipment.
and as the previous poster said DO NOT STARVE YOURSELF!!! every see those infomercials with the starving kids? see the pudgy bellies? that's what will happen to you. you loose muscle, gain fat and then turn to skin n bones. you don't want that.
You should reach your goal of 225 and then some! I'm 17 and when I was 15-16 I weighed 236 at my biggest. I now weigh 175lbs and I feel a lot better, and I'm still loosing more. I just ate oatmeal for breakfast, or 2 organic eggs with turkey bacon. For lunch I ate lots of different things like chicken salad, regular salad (with low fat dressing), Subway, turkey sandwiches on wheat bread or multi grain white, and other things. Turkey, chicken, fruits and veggies are very good to keep in your diet. Stay away from mayonnaise, large amounts of red meats, fast foods, soda, high salt, high fat and sugar. Look for glucose, dextrose, and corn syrup in food labels, because thats sugar in disguise. I only exercised 3 times a week 30-60 minutes (at least 20 minutes of moderate cardio, the treadmill is good) but I increased my workout time every 2 weeks by 5 minutes, but everyone's metabolism is different. You really should try and switch up your workouts/increase the time you workout because your body can be used the workouts and it could become ineffective. Make sure you drink a lot of water 48oz or a day, also make sure you do toning exercises (crunches, squats, leg lifts ect) because I didnt at first and now im left with some loose skin that is very hard to tone!
Hope this helps and good luck!
Ps: DO NOT ... I REPEAT DO NOT starve yourself. You will actually end up gaining fat and losing muscle mass if you do this, so in turn the scale will say you lost weight, but all you did was loose muscle because muscle because it weighs more than fat. If you dont eat anything for 24 hours or so, your body goes into "starvation mode" storing almost anything you eat as fat, because your body thinks your food rations are low and wants to keep you alive.