Unfortunately, you need to approach this much more aggressively, if you want to avoid having to take medication. Concerning diet, there are two options.
The first is a very low-fat vegan diet. A vegan diet does not allow any foods of animal origin: no meat, fish, eggs, or dairy. Since the diet will be low-fat, no nuts, avocados or oils are allowed either. Everything you eat would have to be either raw, steamed, or boiled. You could have fruit, but no candy (even if it's "fat-free.") The advantage of this kind of diet is that there is no limit on calories.
The second option is a low-calorie, low-carbohydrate diet. You would set your maximum number of calories at 1500 to 1800, and your maximum amount of carbohydrates at 40% of total calories, with at least 30% of calories as protein. Another way of looking at it is to set your maximum amount of carbohydrates at 100 grams, or less and consume 1 g of protein for every pound of (your ideal) body weight. The amount of fat is not important, as long as most of it comes from grass-fed animals. However, the amount of polyunsaturated fat needs to be minimized; use MCT oil, instead of vegetable oils for cooking. The advantage of this type of diet is that even though it's low in calories, you won't feel hungry.
As for exercise, you have two options depending on the type of diet you choose. For the low-fat vegan diet, the best exercise plan for maximizing weight loss is aerobic exercise. But you have to think of exercise like a drug: the "dose" needs to be high enough, in order for it to work. You need at least an hour of high-intensity aerobic exercise a day, five days a week. More than that is even better. I know that sounds like a lot, but you don't have to start doing that right now. You can gradually work your way up to that level. As your fitness improves, it'll get easier.
For the high-protein diet, the best type of exercise is resistance training, otherwise known as "weight-lifting." As for the type of weight-lifting, there are, once again, options.
The first is circuit-training; you do a full-body workout, but don't rest as you go from one exercise to the next. You have to move quickly, so that your heart rate doesn't come down. Three times a week should be enough.
The second option is to exercise major muscle groups, one group for every session, five days a week. On the sixth day, do brief sprints alternating with minute-long walks. Obviously, the best way to do this would be work out the legs on Monday, and then do the sprints on Saturday.
The third option is to do a super-slow, full-body work out once a week. The key to doing this type of workout is to have perfect form, and to perform the movements very slowly. You only need to perform one set, as long as you use the maximum amount of weight you can handle. If you choose this option, you have to increase your level of activity also. "Activity" is not the same as "exercise." If your school or work is nearby is within walking distance, try walking there instead of taking the car. When you use the car, park far away from the building. Take the stairs instead of the elevator. You know, small things like that.
These recommendations are based on clinical research.
If you have questions, please feel free to e-mail me.