Sore scalp and dandruff problems :-(

[ChunkyMonkeyMother]

Can anybody reccomend a good anti-dandruff solution?
I usually use head and shoulders but this doesnt seem to be working anymore I have very thick, long hair which I usually wash 3 times a week - I look like I have nits at the moment from scratching and it is getting me down.
I have recently started at an exercise class 4 times a week so I think it could be down to sweating but just don't know what else I can try, have used many different anti-dandruff shampoos but am at my wits end - HELP?!?

have you used dovonex? : its basically concentrated Vitamin D solution

Sorry I always go on about soft water, but this was the only thing that sorted my sore, itchy, flaky scalp. Once we installed a water softener it cleared up practically overnight. When the salt runs low the itch and flakes return.