Don't worry if you aren't there yet, It took me over 6 days to get there, but as I've mentioned before I was eating and drinking a lot right up till I started, due to events I had to attend.
I still remember day 4, feeling so hungry it hurt, day 5 was okish, then suddenly the afternoon of day 6, I realised I didn't want to eat my own arm any more. It's brilliant!
I still want to eat, but as I'm not actually hungry it's so much easier to resist. (That and the bar at supper if I've stuck to it, heaven!)
Hope it kicks in soon for you!