Because this incidence came so suddenly, it is probably just a swollen lymph node. If it was a cyst or even tumor, it more likely would of developed over time. You should still get it checked out. Especially if you are due for a annual pap and pelvic exam.
I had a lump that wasn't painful, on the inner portion of my breast. At my annual pap smear, I told my doctor I felt it. He checked it out and said it was most likely a cyst. He told me to notify him if it changed in shape at all. But not to worry. A year later it hadn't changed, but my mom was diagnosed with breast cancer, so they immediately removed my lump because of my now family history. It turned out to be benign and was just a cyst.
So the moral of the story is, get it checked out any way. Women should get an annual pap and pelvic exam and if they are over 30 should definantely get an annual mammogram.
Hope this helped, best of luck.
Natale

You should have this examined. It's probably just a lymphnode, the way you described it, but this certainly merits attention.


Regards,