How to use shampoo

I have an oily scalp, so I have to wash my hair 365 days a year, even on my days off at home, but even then, it gets so itchy by lunchtime.

I've tried every shampoo that's supposed to be good, but I'm not sure if they actually work for me.

I found out by chance while watching YouTube that they wash their hair just like they pre-wash clothes.

It seemed like the itching was a little less if I washed with a small amount of shampoo and then washed it again.

I have to wash it every day, but it is still one of the ways to last a long time.