Some reasons why you have this problem is missing meals, starvation, or you eat a very low calorie foods. Yes you will get your weight goal fast and soon but your body will detect your low calorie intake and may conserve energy in your body that will stop the weight loss and you will gain weight again. Crash diet is not really healthy but only temporary. I experienced this kind of problem before and I stop dieting because I worked hard for it but I gained weight again and more than what I had before. Janet Jackson is one of the example of Yoyo dieting victim.
Fad dieting will not help you in the long run.
If you want to lose weight permanently, do it slowly and don't go for other alternatives like some gurus who teach fads dieting. Do it slowly but surely. Take a slow approach.
1.0 Losing a small weight gradually is alright. One pound a week is normal.
2.0 If you want to decrease your calorie intake, do it gradually.
3.0 Think your diet as a healthy move, not just a fads or something else.
4.0 Change your lifestyle and food.
5.0 Eating good healthy foods is a lifetime commitment.