lots of us had to do that. You'll just have to white knuckle it. It gets a lot better by about day 4 because your body goes into ketosis at that point. The headache is from carb withdrawal - that should go away as well. Just hang in there - the liquid diet is the hardest part of this.
I found broth, Jello, and sugar free popsicles the most helpful, even though nothing really helps that much. Jello and popsicles were the only things that resembled real food, so I ate them with abandon. And broth has salt in it, so it makes you retain water, making you feel a little fuller. Just hang on....this'll all be over before you know it!!