You sound just like me at day 3 and 4 -- horrible. I'm on day 7 and am getting rid of a cold sore from day 5. But I have to tell you, the last time I got a cold sore it was so painful - this time it's clearing up pretty quick. Yesterday I had a foggy mind and today I'm clear. Each day brings new and not so fun things.
Remember though - this is your body fighting back! So yes, it is a normal part of the fast and what you're feeling is normal (well, if you can call it that). I bet tomorrow you'll feel a lot better. Day 4 was very tough for me too.