The first possibility is of a boil or abscess in the area. The second possibility is of a perineal hernia. It is a hernia involving the perineum (pelvic floor), mostly found in men and often appears as a sudden swelling to one side (sometimes both sides) of the anus.
Second possibility which comes to my mind is of pilonidal cyst. It is a cyst that develops along the tailbone (coccyx) near the cleft of the buttocks, more frequently found in men and presents as localized swelling over the lower spine.
Third possibility is of any perianal abscess if there is any accompanying pain or redness over the area.
A physical examination is helpful in confirming the diagnosis.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Im having same problem right now there is a swelling under my perinuem area going to my scrotum im depress ryt now bec i dont know what to do.. Im in abroad far away from my family.. The pain is severe mostly when im walking and standing the doctor gave me antibiotic curam 625mg and diclofenac.. Im on the 3rd day of my illness and still its painful how long will this will be gone..