MomPOm, I didn't have that problem, but I do remember that before I did SBD, I used to eat an entire bagel with cream cheese and 2 pkg of oatmeal, prepared, for breakfast, and I was hungry about an 1.5 hours later. On SBD, that doesn't happen.
I'm not sure about the nauseous feeling (though I think Ruth is totally right if you're taking a multivitamin--most of mine made me feel sick if I didn't take them with food), but I would think that the difference between how hungry you are when you eat simple carbs and how full you are when you eat protein and veggies could be the issue you're feeling, especially if you used to skip breakfast.
If it doesn't go away, you might want to talk with your doctor.