A chronically itchy anus is very disabling. Small breaks in the skin from scratching leak moisture which makes the anus more itchy. Most over the counter creams give only short term relief and can lead to irritation themselves.
A combination of cutting the nails short, washing the anus only with water and never soap, wiping the anus with baby wipes and only using anal creams for no more than 2-3 days usually settles the itch down.