Hair Problem!!! Help?

So in the last couple months, the hair close to my scalp has literally taken on a nasty plasticy feeling when I wash it in the shower (like when you rub a balloon), and my hair used to be really bouncy but now right after I shower, it lies flat on my head. It feels like there's some sort of buildup but I can't see ANY residue at all when I touch it, and I've tried washing it with apple vinegar and changed shampoos/conditioners, but nothing seems to be working. Any help?