This may sound a little off the wall, but I think you should look into doing parasite cleansing.
I recently watched a recorded lecture on this exact subject.
The lecturer recommended getting rid of parasites before making a diet change.
Apparently parasites will get shook up if their happy little home is disrupted by sudden diet change.
When this happens they all pee at the same time.
That means - ammonia flowing in the blood stream. When it hits the head - bad headache!
This should only be the case for someone who may have more parasites than normal. Everybody has parasites ,but this is unusual here on the Master-Cleanse forum.
Thats my take on it. If its true, you will do well by cleaning them out.
I highly recommend Hulda Clark s parasite program and using a zapper with it to handle these guys.
I happen to be doing both right now. Its always a good idea to be clean of parasites.