I had what I'll call HBI (Horrible Butt Itch) for at least 20 years. At least. It was horrible and it affected my life. I often couldn't go to sleep, I would constantly have to scrub my nails in the morning for obvious reasons, etc. It Interrupted my sleep and I'd be embarrassed if I had company or shared the room with someone because I'd usually have to take care of the itching before I could sleep. I tried pretty much everything you could imagine to cure it or even reduce it but nothing was a cure. Cortaid with aloe was the only temporary fix but that too had its limits.
Then I decided to get my toenail fungus treated. The doctor zapped them with a Lazer, gave me a topical treatment and prescribed terbinafine for a month. Next thing I know, I was cured. The itching stopped - virtually within a few days or weeks... I'm not sure because I wasn't expecting it and I just kind of noticed. I didn't realize it at first but it had to have been the terbinafine. I swear that's what did it. I must have had some internal fungal infection that it cleared up nearly overnight. (And fixed my toenails too!)