This boil, or more correctly folliculitis, occurs quite commonly in areas where the hair are forcibly removed. It is the result of traction, leading on to inflammation, and bacterial infection.
First thing is to avoid any method of hair removal; though clipping might be a suitable alternative. A topical antibiotic, like Mupirocin, will hasten the healing. But please continue to use the antibiotic cream at least for 6 weeks after your 'boil' has subsided. This will ensure that any remnant bacteria left on the skin surface on that area are not allowed to thrive. I am sure this will solve your problem. Sometimes, you may require an oral antibiotic. Please consult a doctor in person for advice on oral antibiotic.