Why aren't I losing weight? Is it possible that some bodies are not meant to be slender and athletic?

I'm a personal trainer, not a nutritionist, but you need protein , especially with the amount of exercise you're getting. Ideally you need a ratio of about 1g of protein for whatever you want your ideal body weight to be i.e. if you want to be 150 pounds then you need 150 grams of protein per day (even on days you don't work out). Protein will help you build muscle, and the more muscle you have the more calories your burn, even resting. It will also aid in your recovery process on off days. Your protein should be had from healthy sources, lean meats and low fat dairy with protein shakes to supplement. You should also be aware of the risk of over-training, and should take at least one day off a week and/or 1 week off every 4-6 weeks.