minoxidil made my head itch for a while too, but I think that with time my scalp adjusted, and perhaps with Nizoral usage, it subsided. My scalp used to itch a LOT before I started treatments, I think it was the irritative action of the male pattern baldness process that was causing it.
Anyhoo, I have a few suggestions, one is a more long term approach that actually also helps the thickening process, and another is a short term fix.
The long term addition to your regimen might be to consider a copper peptide spray. The most popular two are Folligen and Tricomin, both have different "feels" to them on the scalp so if you are interested in trying them you might consider trying a little of each and seeing which seems to have a better fit. For an irritated scalp, I would recommend Tricomin as it has a shot of menthol in it that has an immediate calming effect on itch... but by saying this, I am in no way saying that Folligen is any less as good as Tricomin is, at least theroretically. Some people swear by either of them, depends on what works best for your scalp in particular.
For an outstanding short term fix, I HIGHLY recommend trying T/Gel "Stubborn Itch Control" shampoo. It is the standard Neutrogena T/Gel shampoo, but it packs a very powerful menthol punch that numbs up even the itchiest scalp, pretty much kills all itchy sensations, period. It has the anti-fungal benefits of T/Gel, which is tangentally beneficial for creating a good scalp environment for regrowth, but really won't help make the hair grow in and of itself.... but, it KILLS that itch! I can vouch for this product personally, keep a bottle in the bathroom cabinet and use it sporadically when my scalp starts to bother me a bit.