Lump inside vagina, hurts when I touch it?

When I was taking a shower, I noticed a lump in there. It was the size of a small marble and hard, hurts when I touch it. It's under the skin and I can move it around a bit. I haven't gotten my period since I found it a few days ago (it was due) but I'm a virgin so I'm not pregnant. It's also not an STD for sure. Please help, I'm kinda freaking out. I researched and it's supposed to be a cyst but I'm not sure.