I think Squeaky Clean was right about the fast uncovering a latent sinus infection. One of the benefits of prolonged fasting is the breaking up of mucus in the system. As the mucus began to break up, you probably stirred up some infection that was lurking in your sinuses. You can buy a saline solution nasal spray pretty cheap at stores like Walmart that might help until you can get where you can do deep irrigation. If you have a stove or hotplate you could also boil water and inhale the steam, be careful not to burn yourself. Last month I got over a sinus infection which was pretty bad using turmeric capsules (homemade), cayenne pepper and a vaporizer. It worked every bit as well as a round of Antibiotics . I know you are a water drinker, but make sure you stay hydrated. Also avoid dairy foods, they are mucus forming.
Hope you feel better soon.