Have you been massaging your scalp a lot?
My scalp hurt/burnt sometimes from massaging it so much as CG required.
In the CH book it said that as the scalp heals it can itch. I am not sure if that was was ever my case though. I have never had a problem with my scalp on sulphates either.
You can also try that sugar scrub as is talked about in the CG book. Put some sugar in your conditioner an rub the scalp with.
My scalp actually itches more as it gets oily.
So I would suggest trying different stuff and see what helps you.