These are pimples caused by irritation from a pad. They hurt, but are not serious. Just be sure to keep the area clean regularly during your period especially. God bless - Blu
It sounds like a boil to me. I use to get them too. In my groin area and in my armpits. They hurt like hell when you squeeze them. Look up boils and it might say something about carbunkles too.
It's probably a zit, but on your private area. If you shave, stop, because shaving creates more opportunities for ingrown hairs. Some people get acne near there periods, so maybe that's why they come at that time. You can do warm soaks on them, either by taking a warm bath or by using a warm washcloth. If there's a hair in the center, try tweezing it to keep it from getting re-irritated. Don't use any harsh or scented soaps on the region, since those can be irritating to the skin. You should also talk to your doctor, and ask them if birth control might be a good idea, since that's sometimes used for period acne.