My itchy scalp is driving me MAD!!!!

I've suffered with dermatitis on my scalp for years. I don't get it very often, but when I do it makes my life an itchy hell. My scalp from the crown to my hairline on the back of my head starts itching, then it makes itchy lumps (which I then scratch) and then it burns! That is normally how it is... today though, for some reason my whole head is one huge itch... it really is driving me insane and for some reason my whole body seems to feel itchy, too! This is what I have (though not as extreme as the top picture!) - Seborrhoeic Dermatitis

I have done nothing out of the ordinary, eaten nothing unusual, not changed washing powder/fabric softener or shampoo/conditioner (the ones I use do vary, but they are all brands I've used before without problems). I'm also not under any undue stress or strain (well, not that I can think of anyway), so why it's suddenly come on today I have no idea.

What usually happens is that my head gets hot (it is worse the longer my hair is) and I have to cut my hair off to about an inch from my scalp and then it eases and disappears. Maybe it has something to do with the air getting to my scalp, of maybe having longer hair just makes my head too hot. My hair gets greasy very quickly, and I have to wash my hair every day or it looks a total mess... and the longer it gets the more of a hassle everyday washing is (and sometimes if I put my hair up whilst it's still wet it doesn't even really have a chance to dry out before it needs washing again... drives me nuts!) - so I try and leave it longer, but I'm wondering if that it worse as the grease from my scalp just sits there and is probably making things worse.

One of the few things that always seemed to stop the itching was to colour my hair (permanent colour, something to do with the peroxide), but I only did that less than two weeks ago, plus I haven't been paid yet, so have no money for the dye.

The only thing I've done that I wouldn't normally do was get caught out in the rain yesterday. I was coming home from a school run and got caught with no hood or umbrella, and my head got soaked. In the past getting rain on my hair just made it greasy (I have no idea why) but I'm wondering if something in the rain water could have reacted badly to my scalp chemistry (or something like that?!). It's all I can think of.

I feel an extreme haircut coming on... if nothing else it will solve the problem of getting rid of the black hair and getting my natural colour back... I am loathe to do it, though, as I really hate having super-short hair, and I just know that everyone will laugh at me for it **sigh**

I could cry right about now, I really could, out of total frustration!