Hello,
It can be a boil or a cyst. If there are more sores and they turn into open sores then herpes should be ruled out. Boils are caused by infection of the hair follicle by staph aureus. . Hair follicles that are blocked by greasy creams, petroleum jelly, or similar products are more vulnerable to infection. Bacterial skin infections can be spread by shared cosmetics or washcloths, close human contact, or by contact with pus from a boil or carbuncle. Treatment includes antibiotics and incision and drainage and do not touch or pick them up.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It could honestly just be a pimple, cyst lesion or whatever. When I was your age I used to get them sometimes too. Tested regualry, never an STD. As I'm sure you've heard many times your body is going through a lot of changes and things happen.
I'm not a doctor so I can't tell you it's nothing. If it persists or you notice it getting worse than consult your doctor or OBGYN
ALSO if you are sexually active it is wise to be tested regularly. Every 6 months or so as long as you are being safe. Condoms are a girls best friend.