It is very likely that you have something called a Bartholin's cyst. This happens when a gland called the Bartholin's gland gets swollen and it can be very painful. Sometimes other small glands can have the same problem. You can try to treat it yourself with warm soaks and sitz baths several times a day, but if it seems to be getting worse with time, or if it is growing or very uncomfortable, you should see your doctor. Most of the time it can be easily drained by your doctor, occasionally it requires surgery to open the gland. There are other possibilities as well, and your doctor can usually tell on his/her exam what it is and treat it. So if this persists, please see your doctor for treatment. I hope this helps, please let me know if you have any more questions.