I am in my 3rd day of preop dieting I'm feeling sick and tired with a killer headache... surgery date is Dec 20 2013

Yup, it sucks....seems to get better arounds days 5-6...the headache will go away but darn it's miserable in the mean time.

How long does it actually take the liver to shrink? I've seen some say they only have 2 wk diet

It all depends on your docs rules and every doc is different. Soccer is right after day 4-5 it does get a lot easier. Place a call to your doc and let them know about your headaches. Remember this is one of the toughest stages in this journey and it only for a few weeks.