Hello,
Without examination,confirmation of a diagnosis is tough but it can be contact dermatitis,rash due to friction rub,folliculitis,cysts or fungal infections.
Apply warm compresses,Neosporin ointment and calamine lotion and avoid messing with it.He can take anti-inflammatory pain killers like ibuprofen or acetaminophen.If the lumps persists then it will be best to get it evaluated from a dermatologist.
Hope it helps.Take care and pls do keep me posted on how your boyfriend is doing or in case you have any additional doubts.Kind regards.
monilial infections are common and it can develop easliy despite your neg result,because they are common organisms found in the vagina and at that certain point your test was made it was not present in that area.Canesten creme helps.