I had a hard time with day/night mix-ups, too. I had to work really hard to get LO to "see the light," so to speak. I would take him out of bed, make him less warm and cozy. I'd remove his blankets and take off his nappy, as well. Somewhere, I read that washing his face with a cool wash cloth would help. It did, and he hated it.
Keeping him awake for a few minutes after a feed and changing his nappy halfway through a feed helped, too. I usually changed his nappy in a cool room, and didn't cover him up much (I know that sounds awful).
During the day, I let him sleep in his travel cot near a window that I did not cover up, so that he would associate day with light. I do cover his windows at nap time now, though.
I was able to change his pattern in about a week. I think (if I remember correctly because the first five weeks were a blur) that I started at two weeks and had him on a loose schedule at three. I was also waking him roughly every three hours to eat.
Good luck! We just made it to two months here, and I can say the first six weeks were tough.
