Going to bed at 3, 4, 5am? Tired, sleepy, grumpy during the day? F.lux is a program for your computer that adjusts the screen depending on the time of day which makes you feel naturally more tired, the dimmer it gets.
There are a lot of customizable features and dimmers you're in control of, so don't worry about it being noon and the screen adjusting to 11pm. It's also pretty lightweight, and in about a week or so, you'll probably start to feel naturally more tired the later it gets!