Was last week your first week? Big losses in the first week are common if you stick to your plan strictly, but you won't see losses of the same size in subsequent weeks.
In my experience, eating junk food makes your body retain water, and slows down your digestive transit time. Stop eating junk, and you get a few good poos out of the way and stop hanging onto all that water. I lost five pounds in two days last week just by swapping crisps and chocolate for yoghurt and fruit, and it felt amazing, but it can't be maintained - there's only so much water and poo in the body, after all. So it's not odd at all that you've only lost a pound this week. In fact, it's excellent progress and shows that you're doing well - those first five pounds were probably mostly just water as your body stabilised, but this week's pound is fat loss.
As for Christmas - yes, you'll probably regain some weight by the scales, particularly if you eat delicious junky Christmassy foods (and you might as well, it's only once a year). But then afterwards you go back to your healthy eating and lose the water weight that Christmas has made you put on, and get an awesomely happy moment seeing the scales plummet.
Not currently trying to lose, as I'm a bit busy building a baby.