Hey George,
Sorry for the delay with replying... just got back from my holiday

First thing we should try top get to the bottom of is why your head ache was so bad....... normally they're not THAT crippling!!...... can you write down a typical days food before you started this diet, then describe what you were eating the day you felt ill........ perhaps if there was a REALLY big change eg from terrible junk to a plate of lettuce leaves, then we can maybe say your body was struggling to adjust!!
Secondly head aches are completely normal when your body is ridding itself of toxins...... you just have to wait it out, and it doesn't usually last long (2 days for me if i remember rightly). PLenty of water and fresh air will definitely help, and paracetamol wont kill you as a last resort!!
Let me know what you've been eating
Nicki