What are some ways a woman could end up with vulvar folliculitis to the point of needing an antibiotic?

Shaving?: Shaving is often the cause of folliculitis. Have you seen your gynecologist about this? I would get in and get it checked asap. In the meantime, don't use the same towel multiple times, don't share towels and don't wear the same pants more than one time without washing them in hot water. Staph infections are more common nowadays and some people are more prone to them. Use antibacterial soap daily.