Congratulations on making it through the first 3 days CAA ! Its all mostly downhill from there on out. for the headaches or bouts of light headedness you may want to consider Sipping on a little bit of potassium chloride or table salt in warm water or mixed in a tea, it should help to bring your blood Sugar back up.
I am on day 2 of a thirty day fast, so far so good ! I was a bit head achy on day one but I usually am, I've fasted before so i kinda know what to expect. the longest I've ever gone was 42 days of only water and the occasional hot tea with potassium chloride mixed in.