Hello,
Without examination, confirmation of a diagnosis is tough but it can be contact dermatitis, rash due to friction rub,f olliculitis or cyst.
Apply warm compresses, Neosporin ointment and calamine lotion and avoid messing with it. You can take anti-inflammatory pain killers like ibuprofen or acetaminophen. If the lump persists then it will be best to get it evaluated from a dermatologist.
I hope it helps. Take care and regards.
i have noticed a small bump on the bottom head of the penis