You may need to drink even more water--Are you taking vitamins? Try the Atkins shake mix, it has all you need, plus potassium. If meat turns your stomach, try chicken or turkey with veggies.
If you lost that much, it was water from carbs. You may need to increase your carbs a few days, up to 30 and see if you feel better.
The hot feeling is normal
See how you feel in a day or so. You can always call the Atkins center and they will help you figure it out. Atkinscenter.com.
Hope you feel better.
Nan