I suggest you drop the shampoo all together for a while.
I put a bunch of conditioner in my hands and massage it into my scalp and hair and rinse then repeat it, while it's in my hair the 2nd time I comb the tangles out.
I was clawing my head until it was bleeding and getting scabs all over it. I hated washing my hair and I'd used anti itch, medicated, and hypo allergenic and still, it was itching just as bad, if not worse.
I read on my niece's pintrest page about co-washing hair. I messaged her on FB and asked her about it.
She told me her scalp had been itching too and she'd switched to washing with a lathering conditioner and it made it worse. So she'd used a simply conditioner for dry hair and it stopped itching in days.
So I started using my Dove conditioner for dry hair. I do not have an itchy scalp anymore. I have lucious hair that's shiny and fluffy and gorgeous.
Have you ever seen those commercials where they notice something is different? I had people at church stop me and ask me what I was doing differently to my hair. It's curlier and swings and is soft to touch.
I use only conditioner, not a lathering one or washing one but a plain old conditioner.
My daughter argues with me that I MUST be using shampoo because putting conditioner on my head without it being clean would leave a greasy mess but I proved her wrong. She still has issues with doing it on her own hair but I "washed" my hair using only conditioner while she was here and I told her to make sure there was no shampoo in my shower, only conditioner, and then I went and did my stuff. When my hair dried, on it's own, she felt of it and was surprised.
I was sick for the last week and didn't feel like showering. So my hair was pretty greasy yesterday. I used only conditioner and when I "washed" my hair in the shower yesterday I felt like I'd have to come back today and wash with shampoo but after letting my hair dry yesterday it was just as nice as if I'd been cleaning it every day.
So conditioner works to clean the hair. I'm not sure how it does it but it does. I stopped itching and clawing my hear. I have several little bald spots on my head where I'd dug so deep I removed the hair follicles. I don't itch anymore. The conditioner stopped this.