Hello,
Without examination, confirmation of a diagnosis is tough but it can be folliculitis,cyst or thrombosed lymphatic vessel. Although less likely but Mondor’s disease has to be ruled out.
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 urologist. Doppler ultrasound may be needed to confirm the diagnosis.
I sincerely hope that helps. Take care.
just to add can not be std as i havnt had sex since my last std test wich results were clear thanks people