Hello,
Thanks for posting your query.
You are most probably suffering from a carbuncle or abscess due to skin infection on your bum .
It's a common condition which occurs due to inadequate hygiene , moist humid climate and sensitive acne prone skin.
Most small acne heal spontaneously in a few days but if it's size and pain keep on increasing it indicates that there is pent up pus inside which needs to be drained . The best solution is to consult your doctor for prescription antibiotics like oral amoxicillin / Cefixime and local antibiotic ointments ( mupirocin or neosporin etc) to be applied twice daily . However in some cases if the condition doesn't improve then local incision and drainage of pus ( I&D procedure ) might be needed to be done by your doctor .
Apart from this you should maintain good hygiene , avoid bandage or occlusive dressing on the lesion , try hot fomentation to help early discharge of pus ( apply cloth dipped in hot water or take hot sitz bath.
For pain mild analgesics like acetaminophen or ibuprofen can be taken thrice daily which will also help with any swelling locally.
Hope that answers your query.
Please feel free to clear any further doubts ..
Regards

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