If you've been relaxed for years, especially if you started as a child, there is a chance you have permanently damaged follicles.

I only had a relaxer for one year of my adult life and the hair that grew back in was kind of off for an inch or so, but nothing that lasted years. This may just be how your hair is now in certain places. I'm not sure and I don't know if this is something a Derm could help you figure out or not. Scab hair isn't a researched issue as of now.