Thank you for your question.
Often pimples on the labia are the result of blocked sebaceous glands that may then get infected. These glands normally function to keep the labia soft and lubricated. Due to a variety of reasons sebum can collect in the gland when the opening gets blocked. Rarely they need to be removed surgically if they are so hard that the prescribed antibiotics etc cannot penetrate deep enough to heal.
I would suggest that you see your gynaecologist who can determine the best course of action so that the infection does not spread to other glands.