It sounds like jock itch
Jock itch is a fungal infection. Antibiotics won't touch it.
Lamasil has treatments over the counter for athletes foot and jock itch. I've used it on both and it works. The vaginal cream might be stronger. Vaginal infections are fungal (yeast) infections too.
Lawn workers catch these types of infections more often because of our exposure to their sources in the soil.