The # 1 culprit in recent times, is EQUAL aka ASPARTAME!!!!! It is poison, and if it is in a diet drink, I am doomed for a headache so bad I can't move my head. I have to check all labels for this. I drink Diet Rite soda now.....no aspartame, no sodium and no calories. It also tastes better than any diet soda out there, to me anyway.
For anyone reading this who suffers from terrible headaches, please watch out for aspartame in your food or drinks. If you must use artificial sweeteners, use Truvia or Splenda....NOT EQUAL!
Using saline solution to moisten or wash out the sinuses really was the key. I believe the saline solution also kills viruses but if nothing else it sure dilutes them.