Hi tikigod,
In theory you aren't more likely to have a fissure than anybody else - BUT, be careful of the steroids, because supposedly they can thin your skin, and maybe COULD predispose you.
OTOH, you need to cure that itch, and the present torment over-rides future worries, doesn't it? Just, be careful and watch your diet, which you already plan to do.
So glad you don't have a fissure. That's good news.