Hi and welcome to the forum.

You say that your weight normally fluctuates. Do you always way yourself on the same scales, at the same time of day, and wearing the same things? If not, you should do. Your body changes in weight by 4 or so pounds during the day. I am always about 4 pound lighter in the morning than when I go to bed. The best time to weigh is first thing in the morning after you have had a "wee".

With regard to weight loss on Atkins, if you have lost 6 pounds in 2 days then much of it will be water weight. A truer picture will emerge at the end of the two week induction. People loose anything from 3 to over 12 pounds, depending upon their metabolic resistence.

Provide you are following the guidance given in the book and drinking plenty of water - to flush that fat away - you should be fine.

Every success.