The scale is a tricky, tricky thing. I don't know how frequently you weigh, but it helps to weigh at the same time in the day every time you weigh. Most experts recommend weighing right after you wake up and use the bathroom for the first time in the day. This way, you can get a more accurate understanding of how much you really weigh. I know that I gain at least two pounds every day if I weigh first thing in the morning and right before I go to bed. But the next morning, those two pounds are gone again, and if things are going according to plan, a little more will come off as well.
You also don't mention what kind of exercise you're doing. Beginning a strength training regimen will almost always mean an initial gain of water weight. If you are doing strength training, or even exercises that are building your muscle, you may be seeing some of that. The water weight will eventually go away, though, and the long-term benefits of exercise are so high they are tough to even quantify.
Cheryl also mentioned other reasons why the scale will vary. The fact is, the scale measures all of your body mass - organs, tissue, fat, muscle, undigested food, etc. - so it will fluctuate. The key is to start learning about how your body works and reacts to the scale. And the only way to do that is to continue with your plan and keep track of how your body is reacting to the choices that you are making with food and exercise. If you haven't already discovered it, fitday.com and thedailyplate.com are good places to track these kinds of information.
You may also want to incorporate alternative ways of measuring your progress. Most 3FC'ers will measure their bodies to see if they're losing inches, etc. Body fat percentage is another good tracker.
Great job for staying on plan for your first week! That first week tends to be the toughest, at least for me.
Wedding challenge - 06/09/2015 - 08/09/2015
Biggest Loser Challenge (12/29 - 03/16) - Not successful. =(
Trainer boy challenge #3 (11/11-12/11):
Not successful. =(
(Trainer boy challenge #1 completed 09/11 - down 23.2 pounds - starting weight 239.8) (Trainer boy challenge #2 completed 11/11 - down 23.4 pounds - starting weight 216.6)