You probably have a buildup of something in your system that a Water Fast won't remove. I have yet to do a really long Water Fast but I finally found the solution to my bad Acne problem by supplementing a high dose of Iodine into me diet. I think the root cause of my Acne was a buildup of bromide and fluoride in my system. I'm not positive but I don't think a Water Fast would do much to remove these toxins. Though if you are toxic with bromide you will experience Depression along with a myriad of other symptoms. I encourage you to check out the Iodine support forum //www.curezone.org/forums/f.asp?f=815
and post about your situation there. You'll find there helpful and after doing some research I believe you may just find what you need and will be able to experience the full benefit of your water fast after a month or two taking iodine.
on a side note. my Acne got worse before it got better while taking iodine. so don't freak out if that happens for you.