From the location it could be a Skene's gland infection. If so, soaking in a hot tub could help it drain. Good luck.
It could be an ingrown hair, it also could be an STD. Being that it hurts it could be an infection, you should make an appointment with you OB.
Im not a proffessional Kayykayy...but if its a lump on the outside it could be a boil.....i have had many through the years....BIG ow! If its a boil it may take some time to come to a head...I have had a few with as many as EIGHT headsI usually take care of my own by checking on them day and night....sitting in hot water..as hot as you can take will sometimes bring them to a head quicker. If that doesnt help me...I find a friend to break open the heada with a clean needle then i put a very hot black tea bag on it to pull out the infection. Once they start draining..the worst of the pain goes away. Dr.s also have stuff that helps it drain and they can lance it in the office.....yeeeouch! I am a wimp so i do my own.... gritting my teeth the whole time lol! Hope it goes well for you...let me know? Keepme