I'm wondering if what you were feeling was just the opening to the vagina. If you felt pain when your nail touched it, then that makes me think that was what you touched. Your symptoms sound like a yeast infection, but if you've never had one before, it would be a good idea to see a dr to confirm the diagnosis. Since you're a virgin, it would be a virtual impossibility for it to be any kind of STD, but better safe than sorry, I say.