working late nights can make you want to drink and eat things high in sugar, also cafffine. you make not be sleeping properly, you must make sure you get your eight hours sleep during the day, try to eat healthy and see if it makes a difference. also your body clock may be out, make sure you are moving your bowels every day (pooping)
I worked at night for many years and found it quite enjoyable.
It takes a long while for the body to become adjusted to this kind of a cycle. It involves re-setting the circardian rhythym.
Give it time.
And make sure you don't spend the day partying, instead of getting rest.