I had headaches as well, but found it was due to dehydration which was weird cause i too drank at least a gallon a day. However, what i came to learn was that drinking water was not enough...proper sodium intake was needed as well. I eat so clean that if i dont add sodium, i become dehydrated. I now add propel packets or pedialyte to my water to get in the needed sodium and electrolytyes for proper hydration.