I have tried soooooo many anti-dandruff shampoos (many of them I have reviewed on BR!). In general it is the active ingredient of pyrithone zinc that seems to work at fixing what is a medical scalp condition.
T/Gel always clears up my scalp, but is very potent and strips the hair of any natural oils. For this reason I would only use it every second or third wash, and use a more gentle anti-d shampoo the rest of the time. It really makes your hair feel (literally) squeaky clean, but also very stringy and tight. For this reason, you definitely need a deep conditioner afterwards, and maybe even a leave-in conditioner for the ends of your hair.
Many people would be put off by the smell of T/Gel. I do hate the smell as it is strongly chemical. But the results are worth it, and the smell doesn't linger on your hair if you use a yummy conditioner afterwards.
One of the weird side effects of pregnancy is your hair type changes. My scalp got SUPER sensitive and my hair got really oily so I had to change shampoo and conditioner. I found this on the supermarket shelves and haven't given it up yet (11 months post partum). It soothes the itches - I didn't suffer from dandruff, just a very itchy scalp - and it lasts in between washes. It's also great for tackling my now oily hair.
The only downside is I find my hair gets quite staticy and light, so it tangle super easily. A good brush helps but I'd recommend not washing your hair and going to bed with it damp because it is a nightmare in the morning.
I've found I need to wash my hair less, using it about once a week. It's also lovely for my skin on my hands etc which are prone to eczema, this does not set me off or cause a reaction.
If I've left my hair a little bit long and it's super greasy I do have to use it twice, but that's a small price to pay for super clean, shiny hair.