Lately I've been getting a bit of a dry scalp and I had been itching for months and eventually I was fed up of it. I got somebody to have a look at it and they said that it was dry and was quite scabby in places as I had actually made myself bleed. The first thing I did was switch my Aussie Miracle Moist shampoo and conditioner for a medicated shampoo, namely, Heads and Shoulders (The eucalyptus one especially for dry scalp). After two washes my head stopped itching as much but it may be longer for you as I have a very bad habit of using WAY to much shampoo/conditioner. As this has helped me and the itching has stopped now, this is all I do. But one thing I heard about that helped people was an apple cider vinegar 'deep cleanse'. Wherein you fill a bottle with a small hole at the top with cider vinegar and completely saturate your hair with it, just, make it literally dripping wet. Cover your hair with an old t-shirt and sleep with it in, then wash and condition your hair the next day as usual. Continue to do this for a couple of days until at least 90% of your dandruff is gone. Then just do it every few days for as long as possible, this should keep the dandruff away.
I don't know how well this works so if any of you do try it then comment how well it worked as I haven't done it myself. I hope this helps! c: