TheFallenChampion
WOW, first off, Congratulations!!! :-) [I must admit that I am VERY jealous; for I've failed miserably, 5 times over, during the past 1.5 months, and my longest fast was just shy of Day 4...]
Anyways, regarding your question, I can totally relate! Some get headaches, some people have nausea, and some (like you... and ME!) fatigue. Fatigue sucks bigtime, and it’s what caused me to break my first few fasts. Some will argue with my method, but I've found that taking a mild stimulant product really helped. The product I used is
http://www.pomology.com/Prod_Energy.html
It's more along the lines of "natural" energy (as opposed to some of those stimulant crazy formulas that the fitness industry markets). Additionally, it provides some antioxidants, which will certainly benefit!
Just be careful if you’re prone to muscle cramping. Drinking water helps. I’m very prone to muscle cramping, even if I drink gallons of water/day; but I’m lucky to be taking hCG, which annihilates muscle cramping.