or at least we were about 20 years ago (for me, not you).

I would often look red in photos (made no sense), would end up brassy (yellow head), would find that my hair would suck up colour and then it fade out quickly (except for the brassy tones).

I've also done some many highlights and ended up looking like a candy cane (white highlights with a 'strawberry' blonde dyed base).

In my million years of dyeing this head of hair, I've now come to the conclusion that my hair hates being lightened - it become incredibly dry, will visibly split like a feather, down the hair shaft. When I darken my hair, brass is left behind.

I'm now walking away, for the second time, from dyeing my hair and am really enjoying my own colour. It actually suits me, go figure

As Firefox said, shampoo isn't meant to condition. Some hair hates oil - hair can look happy but then suddenly feel like straw.

And as the other poster said, also consider having a check up to rule out other health conditions.

Maybe consider taking it 'back to the basics' - finding an inexpensive, gentle, sulphate free shampoo, as well as a good, silicone free conditioner (then you won[t need a harsh shampoo to wash out the build up from certain silicones)? And treat your hair gently and kindly. If nothing else, such treatment won't further damage your hair.
Growing out a pixie (last big cut July 2012)
3a? 3b? Fine, dense. Porous.
Finally sulfate free. Avoiding silicones.