Hi, I'm not sure what kind of fast you're doing, but restricting caloric intake can certainly slow weight loss. It gives the body the message that there is a "famine" and so it goes into insulin resistance to try to store fat. Losing weight is not just a simple matter of taking in fewer calories.
I'd suggest that fasting isn't for everyone, and can actually be weakening if done improperly. For losing weight there are methods that work with your metabolism to shift your hormonal balance safely so that you're burning fat. But it's not a one-size-fits-all method - no one diet is right for everyone. You have to work with your own biochemical individuality.