Heres a link to some herbal remedies that might help: http://www.hipforums.com/newforums/showthread.php?t=336666&highlight=herbs+for+your+head&f=209
ACV can make your scalp itchy. It changes your scalps Ph, which can be a scratchy process...Rinse, rinse.
Yeh I'd suggest another thorough rinse, and maybe try washing with nothing next time, see what happens.
Water isn't nearly as good of a solvent as shampoo. Hence shampoo will get rid of more junk than water. I feel like water is good for frequent washings but when its been some time shampoo will do more justice.
I think Pat's got it. Too much baking soda. If you take the BS route you only need about a tablespoon to a big glass of hot water. Then rinse with plain water, then rinse with 1 part ACV to 6 or 7 parts water. Or, you could always just cut your scalp off. Then you won't have to worry about it (your scalp) itching ever again.