While most people make most of the adjustment to fueling their body on low carb within the first couple of weeks, it can take longer for some people or more moderate adjustments continue to happen for weeks.

Make sure you're eating enough protein. There's lots of emphasis in many LC discussions these days about eating lots of fat, but I think sometimes people don't eat sufficient protein. My introduction to LC was in Protein Power and they follow a common formula for minimum grams of protein per day that you can find around the web:

• Sedentary - multiply lbs of lean body mass by .5
• Light activity (e.g. walking) x .6
• Moderate (30 minutes of vigorous activity 3 days per week) x .7
• Active (1 hour per day 5 days per week) x .8
• Very Active (10 hours of vigorous activity per week) x .9
• Athlete x 1.0

They suggest that obese people go to the next highest category because you're doing that level of activity with extra weights.