Darn...wrote a long post but it got lost.
, I would concur with the Beachies who point out that your sleep deficit is much more likely to be the problem here. I eat a snack around 2 when I stay up that late, but it doesn't seem to lead to any gain.
Lack of sleep keeps your body from doing the things it usually does overnight to help you lose weight and
results in your body producing hormones that lead you to snack more (usually it's a craving for simple sugars, too.). Consecutive sleep is best here--naps will help--but you want to aim for consecutive hours of sleep as much as possible. It's REM sleep that gives you the most benefits in weight maintanence and loss, and you can only get REM sleep if you have a long stretch of uninterrupted sleep. To get to REM sleep, your body goes from level 1 to level 2, then levels 3 and 4, and finally to REM. If you wake up at any point as you go through the levels, you start over again when you go back to sleep (this is why people with sleep apnea are so tired...they have trouble getting to REM sleep because they wake up each time they stop breathing).
Are you parenting with a partner? If you're breastfeeding, could you pump so your partner can give the baby a bottle for the day's last feeding while you go to bed early? Then you can get up when the baby's next feeding/wake up time happens. Several of my friends who are moms employ/have employed this strategy successfully. In time, you'll get into a routine and get more sleep--until then, just try your best to eat healthy and get as much sleep as you can.