I have a reoccuring patch on my scalp, that comes and goes at random.?

towards my "widdows peak" on my scalp, i have a spot. Its very difficult to explain this to anyone since it comes and it goes, and ive made appointments for this issue, and the following day when i go in to be seen, its gone.

I first noticed this after getting ready for my highschool prom. that was over 10 years ago.

the patch seems to have no real explanation... I wash my hair usually with the same products, and go a few weeks at a time without any issue, and then all of a sudden, this spot will appear to be greasy and wet. it will itch like crazy, and feel sticky. I fight to leave with myself not to scratch at it. when inspecting it, nothing is there, other than redness. theres no indicator of where the patch starts or ends, or where the fluid appears to be coming from. theres no holes, no sores, no nothing. just redness and clear sticky crap on my scalp only in this one spot. It always only happens on this one spot. the following day, the ichyness and redness is gone, and large (sometimes even dime sized) flakes of skin come off of my scalp in the spot. they are large enough so that i can slide a comb underneath them, and comb them out fully intact once my hair slides through them. Under them generally is normal scalp. no irritation, no more flaking, nothing... until the next episode.

I thought this was an issue with products. So i have changed and changed my shampoo and conditioner a million times, and it still happens. ive even used baby shampoo, organic stuff. everything. i have settled on using DOVE, since it seems to have less frequently (about once a month now) while using this.

so, what could this be? Its annoying as can be, and nobody seems to have any idea. Ive been told exzema, psoriasis, and all the other cleche' skin conditions. but thats not right. Anyone else experience this?