Maybe just a sore from rubbing or maybe std so many things it could be I would find a dr. and if you can not do that and need to be discreet their are free clinics for teens look on the web in your area and get help if it doesnt go away.
Hello,
Without examination, confirmation of a diagnosis is tough but it can be contact dermatitis, rash due to friction rub, folliculitis, cysts ,molluscum
depression or plug) or genital warts(caused by HPV infection).
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.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.