Hi, Thanks for the query. The possible causes for your lump are: Folliculitis which occur due to infection of hair follicles. Clogged sweat glands can form as lump and when they get infected presents as painful lump. Infections like warts, herpes, molluscum contagiosum etc cause lump on labia majora. Any type of infection should not be neglected in pregnancy as that can affect the well being of the baby better to consult gynecologist and get examined to find out the actual nature of the lesion. Depending on that treatment can be taken. Take care.