Welcome to Healthcare Magic Hi I am Dr Fahim and I will help with your Query I have gone through your question. What I perceived, your primary worry is development of melanoma in the lesion that you have. Melanoma is the carcinoma of the melanocytes present in our skin. Exposure to sun is one of the triggering point and it usually develop in mole and naves and are not painful. Your lesion is not in the sun exposed area and its painful so to me, It appears to be sebaceous cyst that got infected or a boil. Which needs treatment with surgical excision under local anesthesia along with antibiotic cover. I hope you will be fine in a matter of days. To be more safe, go for histopathological examintation of the removed specimen which will give us cleat cut diagnosis. I hope this will help you. Do rate my answer if like it. Regards