From your symptoms,it looks like a Bartholin's abscess or cyst. There are glands in the vaginal lips called Bartholin’s glands. These can become painful and swollen, and an abscess can form. This often causes blockage in the main duct from the gland, and a cyst develops. This is felt as a painless, hard swelling.In such cases, antibiotics may be helpful, or surgical treatment might be required.
Other possibilities are sebaceous cysts (accumulations of secretions that can occur Fanywhere on the skin or mucosal surfaces), lipomas (fatty deposits) ,fibromas (fibrous tissue deposits) or viral warts(small raised pimples to a mass of large, cauliflower-like growths. The virus that causes them is passed on during sex).