Seems like you have developed Folliculitis
over the groin region
Now firstly i would advise you to keep the area clean and dry as much as possible...Do not apply any kind of moisturizing creams/lotions or oil over the affected area....Wear cotton undergarments so as to decrease the amount of sweating..
Clean the area with lukewarm water twice a day and apply an antibiotic cream like mupirocin
gel over the area twice daily...
If inspite of the above measures, the lesion persists or continues to increase in size, then you might need a course of oral antibiotics
along with pain killers..In that case, i would advise you to visit a dermatologist
for proper assessment and treatment
Hope it helps
Dr Geetika Paul