Caked scalp due to product buildup?

Hi everyone. I use two main products for my hair before I straighten it. I only wash my hair once a week since it is too much of a hle to wash it all the time since my hair gets really damaged and starts to break off. So after a while, I get a buildup of products on my scalp. So bad that I can literally sc it off with my fingernail. It's only a cm or half a cm thick but thats still a lot when nothing should be on my scalp in the first place. My friend had the same problem and said there are a couple shampoos out there aimed to solve this type of problem and I was wondering if any of you knew the names of these products and where I can buy them at affordable prices? Thanks a bunch guys :D I think this caked up buildup is causing my hair to fall out and I want to preserve as much of my hair as possible! Thanks in advance :)