Hang in there.
Is it possible you have a hidden food allergy and you didn't eat it in the past couple of days? I have tons of food allergies (wheat, corn, dairy, etc) and when I start my diet, I cut all of those out. By day 3 (today), I'm going through withdrawl from dairy so badly that I feel like I'm dying. My entire body hurts and is tired and weak. But if I get through it, then I feel so much better. It's possible you are just withdrawing from sugar and that's causing the bad feelings.
Give it another try and try to power through day 3! My plain cellophane noodles, cherries, and water for lunch aren't looking too great right now, but they'll do the trick on filling the tummy.