Your symptoms sound like irritation of the anal skin (often called Anal dermatitis), which can happen from using soap, as that area is very sensitive; the main treatment is to stop using soap or any harsh products. Apply a soothing barrier cream like zinc oxide or petroleum jelly to protect the skin, wear loose cotton underwear, and avoid spicy foods. If the problem is still not improving, it?s important to revisit a doctor (possibly a different specialist).