I'll say it because I don't think anyone else has (if so I apologize).
but the headaches could be sinus related. One poster already mentioned the dehydration, but I'll drink a gallon of water a day and still feel dehydrated and headachie.
Sinus' don't need to be runny or infected but can get very inflamed, irritated and dried out. Pg will suck the moisture out of your nose everytime you blow out.
My sinus were so dried out the pain was extreme, with pressure and pain in behind my eyebrows, between my nose, cheeks, even teeth sometimes.
Sinus is especially painful in the morning because you are newly upright and inflammation or block is keeping the fluid in instead of out and because you may have been sleeping in a dry room. Also, another difference is if it hurts to touch your face where the pain is or your eyes feel dry.
Another good way to tell is if a hot shower, breathing steam, drinking hot liquids will relieve the problem.
At any rate, the solution is more moisture up and in your sinus', but a doctor will be able to tell you for sure. I don't know, something to consider anyway.
You can read all about sinus here -
Sinusitis - Symptoms, Treatment and Prevention
By the way, anyone know the mix ratio on DeKang juices?