My DH had the same problem when he worked 11-7 for a few months.
He blamed it on eating his big meal just before he went to bed, so he started eating his big meal of the day at work and just had a bowl of cereal and skim milk before bed. He slept better and lost the few pounds he'd gained.
However, he also stopped snacking during his shift, so it's hard to tell which was the real cause of his weight gain.
ETA: Ooops, I got to this thread through "new posts" and didn't notice it was in the 20 somethings til after I posted. Sorry about "butting in".