I'm not an authority on fasting, but I've done many 3 day fasts and diets and so on
Your body becomes accustomed to being "undernourished", it uses different biochemical pathways when being "starved" as opposed to when you get enough nutrients and you get them often.
First time I've water fasted for 3 days I lost more than 12 lbs.
It was a shock reaction. My body was not accustomed to this kind of famine. Since then I've done many diets, fasts etc.
I'm now on my 13th day WF, I didn't lose any weight during the first 4-5 days. All in all I've lost 13 pounds, some of it is purely water weight.
It's not great if you try to lose weight, but it's the reality.
Maybe you should try intermittent fasting, it "shocks" your body constantly into weight loss and keeps your metabolism working.
or as Archus says, continue your fasting and you will lose weight. Don't give up, but try being realistic (yeah, I have a hard time doing it as well).