Boils

I have a boil on my bikini lining, but i don’t get how I get it this is the third one I’ve gotten since August and this one is very painful that I can’t wear underwear Bc the tightness from my underwear hurts me. I’ve been told that sometimes you get them because your underwear rubs on your skin and it becomes very tight but to me that doesn’t make too much sense. If anyone understand that logic please explain to me. TIA