I can never sleep, so I find myself staying up late at night like a night owl.
Oh, is there any problem?
Night owl (person)
A night owl, evening person or simply owl, is a person who tends to stay up until late at night, or the early hours of the morning. Night owls who are involuntarily unable to fall asleep for several hours after a normal time may have delayed sleep phase syndrome. 
The opposite of a night owl is an early bird – a lark as opposed to an owl – which is someone who tends to begin sleeping at a time that is considered early and also wakes early.
the middle of the night, probably while he was staying on the third floor of a rooming house at in Chicago: "...it was a late fall night and raining...I was there naked in the bed and I sprang up. I went to my typewriter and began to write. It was there, under those circumstances, myself sitting near an open window, the rain occasionally blowing in and wetting my bare back, that I did my first writing...I wrote it, as I wrote them all, complete