I have a boil kind of thing inside part of vagina , and it is painful , what to do , it's just started?

Bartholin abscess?: This sounds like inflammation of your Bartholin gland, which is one of the glands that produces sexual lubricant; there is one on each side of the vaginal opening. Some but not all such infections are due to STD, especially gonorrhea or chlamydia. See a doctor ASAP; you probably need an antibiotic and maybe an incision to drain pus. Good luck!