A painful bump near the anus that reduces in size over time commonly points to a few specific conditions related to the local blood vessels, skin, or underlying tissues. Possible Causes:-- 1. Thrombosed External Hemorrhoid. 2. Perianal Abscess. 3. Anal Fissure with a Sentinel Tag: 4. Folliculitis or Furuncle (Boil). You can use these conservative measures to find relief while monitoring the area:--- 1. Sitz Baths: 2. Avoid Pressure and Straining. 3. Avoid poking, pressing, or trying to squeeze the bump. 4. A plain protective ointment like Lignocaine ointment can reduce pain. If there is fever, pus discharge, marked pain, or any other untoward symptoms, please immediately consult a General Surgeon.

Looks like infected condition..swelling with white head suggest pus formation like boil may leads to abscess or fistula formation. take treatment as soon as possible.