Have you been getting enough water? If not, too many ketones can cause nausea in some.
Were you a big carb eater before this? If so, sometimes the extreme carb withdrawl effects people. You could try to do the alternate phase 1 plan for a week or two. It is designed for persons adjusting to lower carbs and diabetics.
Are you sensitive to sucralose or acesulfame k? You can test this by using packets with the lowest of either of these levels. See the spreadsheet by I'm Svelting for a breakdown of this information in grams per packet.
Have you checked your blood sugar? How about your blood pressure? If either are off it can make you feel this way.
Are you allergic to soy? Soy is in the majority of these packets and foods?
Are you allergic to whey? It is the second most used ingredient.
What else are you taking with your meals? Any other supplements? Try holding them for a meal and see if the reaction still occurs.
As Svelting suggests, backing into the plan may teach you if you have a tolerance threshold you are exceeding.
Keep us posted on what you learn!
Feel better!