Hello,
Without examination,confirmation of a diagnosis is tough but it can be contact dermatitis,rash due to friction rub,folliculitis,cysts ,molluscum contagiosum(multiple, small, dome-shaped papules, often with a central depression or plug) or genital herpes.
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 pls do keep me posted on how you are doing or if you have any additional doubts.Kind regards.
You can apply vaseline,mostly an irritant reaction.