Its perfectly normal, your body is getting used to having very little in comparison to what you ate before.
Drink plenty of water, and look at how you can distract yourself, have a pampering bath, check out the minimins arcade.. stick with it and you will see the results
i know i worried about it and posted on here last night, i read that there is a condition called water intoxication!! but its quite rare and more prone to atheletes ect not going to have that much again though lol