Barring anything medical, weight gain is usually from taking in more than we are burning off. You need to find a plan you can live with and that will motivate you. Get some fitness magazines and read them for motivation and ideas to help with weight loss. Take a new workout class that you have always wanted. Make a home gym with a dvd, mat and weights. You can even get some out of the library. Go for walks. Tell yourself you are going to stick with it for 3 weeks. You might just choose calories (like 1300) a day and see what happens. Weight loss isn't an exact science and you have to keep changing things up. It takes a lot of time and hard work to get to goal. Good luck!