Headaches are quite normal (common) when beginning a fast. Some people get them as a withdrawal symptom - from several different substances like yeast, carbs, caffeine, refined sugar... Many here have decided to allow themselves to use a pain killer to get them through the first few days. If you can do without, then that would be WAY better. But if the headache is going to cause you to stop fasting, well, do what you have to.
Meanwhile, WATER helps a lot. Drink it until you think you can't drink anymore! hehehe You may experience immediate relief by doing an enema. Try taking it easy and reading a good book, or maybe take a light walk, have a warm bath, drink some herbal tea ... something to relax you. Even a nap may solve your problem. Try and remember that food will not help right now since the body is going into detox mode. Press through the pain and remind yourself that what you're doing for your body is worth it! God bless and fast on!!