Hello shivani, I m assuming that by pimple you mean small bumps filled with yellowish pus inside it. If that s the case it is most probably an infection. Note if the lesions are separated like one pimple at one place and the next at other place at the base of your hair follicle then it can be due to blockage of the glands under your skin which then became infected. I would suggest you to take proper vaginal hygiene, change or wash your undergarments in hot water regularly, use topical ointments like bacitracin or clindamycin along with oral tablet of metronidazole three times a day 500mg. If you have had a sexual encounter and think the symptoms are getting worse then consult your physician for further evaluation.