If you haven't already, and I'm sorry for the delay in a response to your question, you should see your doctor. Often, you'll need antibiotics to clear an infection if it is a Bartholin's Cyst - https://www.mayoclinic.org/diseases-conditions/bartholin-cyst/symptoms-causes/syc-20369976 (The pic here is exaggerated - yours may not look this big.)
There are some other things that this may be, but your doctor will be able to determine what is causing your pain. I hope you've gotten some relief by now.