trying to get 'back on track'

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Recently I have been going out with friends etc, and the alcohol plus drunken eating plus hangovers has meant that my weight has gone about 2.5kg above my comfortable maintenance weight.
Therefore I am trying to get back to that weight, by eating 1800 calories and going to the gym.
However it's 4pm, I've had about 900 calories and am waiting for dinner and I am SO HUNGRY.

I'm hoping this is because my body is used to about 2500 cals but my goodness, it is so hard to be 'good' when I am so hungry!