This lump can be 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. Other possibilities are sebaceous cyst, lipoma, fibroma or viral warts. You should get a gynecologist’s examination done.
I hope it helps. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.