Cholestyramine isn’t a lotion - it gets mixed into a suspension and taken by mouth.
The itching suggests fungus, even though anti-fungals/anti-yeast efforts have failed. 1) I wouldn’t use a bidet to scratch the itch - that’s pretty harsh, 2) make sure to let the area dry and to keep it dry, 3) a dermatologist could easily tell if it’s fungal, and suggest an appropriate treatment.
Some people like antifungal powders, though they aren’t my favorite.