What Causes Red Bumps On Vagina,anus And Armpit?

Hi I am 14 years old 5'4.5" tall, 135lbs with no bad health history. Anyways I've had this thing for probably 2 years now and I get these red bumps on my vagina, butt crack, or armpit. And I have no clue what it could be it hurts when u put pressure on it and I've tried to pop it a couple times the one time I succeeded it just bleed with out puss so I don't think it any zit type infection but I'd really like to know what it is because I'm very worried!