What you are looking for is a long term solution which requires 1) a plan and 2) discipline to follow through with the plan. Plans are a dime a dozen and plans that work with one person may not work with another. But one thing that helps is to monitor your calorie intake. I know this is a pain, but what it does is allow you to make better decisions about what goes into your body. This allows you to fit in those treats or foods that are the healthiest, but you don't feel guilty about eating them.

Regardless of your plan, keep at it. Even if you can't see in results. They will come, and it will take time. Even if you only exercise of 20 minutes, make those 20 minutes count. It may take a couple months, it may take a year, but you have to think long term. Pretty soon 25 will turn into 30. And 30 will turn into 40. And if you don't start now, it will be that much harder later in life. The body does not work quite as efficiently at 40 than it does at 25. Pounds are so much harder to take off.

One last note, stop getting caught up in body size. I ran an 8K last month and there were a number of younger women, probably around your age, with body sizes that were not "fit and trim" that were keeping with my 9min/mile pace. If want to compete to run a marathon, then yes, you might want to be small and tiny, but if you want to be a normal human being, then be focus on being healthy.