Google 'Bartholin's Cysts'. If you are brave enough to view the images of them (warning, they are graphic photos of female private parts) you may find what you have, and be able to go to a website to read more about it. - Blu
It can be infected glands or cysts and bartholin cyst is one possibility that should be ruled out. The other possibility is of herpes sores which are painful.
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 hard swelling. In such cases, antibiotics may be helpful, or surgical treatment might be required.
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.