Hi, Thank you for posting your query, I have gone through your query and understand your concern. Since you have undergone chemotherapy and radiotherapy, I do suspect the reason for pain and itching could likely be infection, it could be bacterial or fungal. The best way forward would be to get yourself examined and get a culture/sensitivity done in case there is any discharge. Meanwhile I suggest you keep the area dry and watch for any swelling, redness, a rash and discharge. I would not at this time suggest any antibiotic or anti-fungal treatment. To help you better, I would like to know for how long you have had this black spot and is there any scaling (dry skin flakes) or is there any discharge(Vaginal or from the labia), or any nodule kind of swelling, do you have any fever. Please do write back describing your problem in more detail so that I can help you better. I sincerely hope this answer helps you. Wishing you a speedy recovery. Dr. Yogesh. D