it may have sometime to do with your fall/winter attire. many of these boils start out as folliculitis (an infection around the hair follicles) so heat and/moisture in this area can be contributory to seasonal outbreaks. i don't know if you are shaving in this area but this too can be a factor.
i get boils/absesses in my pubic area but they only happen at certain times of the year like fall/winter. . they start out as just a small red bump but usually get to the size of a quarter. they make a head and some pus and blood drain out but may remain red and hard under the skin for a week or so.