It souinds like you could have genital herpes.... It can be extremely painful. You can be tested now with an outbreak or simply have a blood test done. Good luck
I would also say a Bartholins Gland Cyst. I get them every couple months. It is a gland inside your vaginal opening that secrets your natural fluids. It can become clogged, and if it becomes infected a cyst will form. The largest I have had it was the same size as yours, It was so painful I could not walk. I had to go to the er and have it lanced. And let me tell you, once it was lanced it felt so much better. It was still painful, but the pressure was gone. If it is that painful you need to go to the ER. Sometimes it will pop on its own and sometimes it will just get bigger and bigger. So you need to call ur Dr. They will also give u antibiotics. I hope you feel better.....Michelle
It's probably just a Bartholin's gland infection. They get large like that and sometimes go away on their own like yours did before. If it continues to get worse check your options on the Net and go see a doctor. Good luck.