Simplest explanation - could it be the water from refilling glycogen from having more carbs? were you super low carb, before?
Percent of what? (how many calories?) I looked at some of your previous posts and you don't say how many calories you were having on Atkins. Also I assume you are still really close to goal.
Do you measure inches as well as pounds?
Are you changing your exercise, such that you might have some muscle weight gain?
How many grams do you have, of protein, carb, and fat?
If protein is low enough, and carbs are high enough, in grams not percent, that would do it for me. What happens is metabolism goes WAY down to match the low protein (body thinks it's hard times), and then with a low metabolism, I can't burn off the carbs and fat I eat, much less use up the stored fat.
Also fruit as snacks (on an empty stomach between meals) stops fat burning for me.