I don't know what might be causing your problem, or mine, but here's a suggestion that was passed to my husband by a clerk, and then to me.
Empty two capsules of Acidophilus & Bifidus into a basin of comfortably warm water.
(I used the products my husband brought home - Natural Factors Double Strength.)
Add five drops of Grapefruit Seed Extract. (NOT grape seed!) Mix, a little.
(New Roots Herbal Liquid Concentrate.)
Place your sitter in the water, and rinse by moving the water over the affected area.
Pat dry. Then smooth on a little Aloe Vera gel.
The first time, I used Lily of the Desert Aloe Vera Gelly (their spelling), but it stung a little for a moment, so the second time I cut a piece off an Aloe Vera plant I have growing in a pot (who knows what variety), and squeezed out some gel. It stung a tiny bit, too, but soon stopped.
I must also admit that I have few basins I would gladly use for a sitz bath. which is what this treatment is called. In fact, I have none. So, I use the bathroom sink. Blush. It is a bit awkward, but I make sure no one sees.
I think that an itch in this area is one of the most agravating experiences known to human kind!
There are several things that can help:
Sit, when you must, on a doughnut cushion; or raise the area off the pressure of a chair seat with two thick towels, folded and rolled, and strategically placed.
The idea is to get the area away from pressure, and to avoid any accumulation of sweat.
A nice 3/4 hour soak in a clear water bath, with 1/4 cup of Pascalite or other Bentonite clay stirred in, seems to draw toxins from my skin and to help the itch condition.
There is a Bath forum at CureZone. Maybe other people's experiences will be useful to you.
Just guessing, would a few days of vegetables and fruit help?