What Is The Small Whitish Blister In My Girl Friend's Vagina?

hello i have a question. I was performing oral sex on my girlfriend when i noticed that she has a sort of whitish lump in her vagina. it kind of resembles a small pimple or a small clitoris. Is this normal? or what is it? is it something to be concerned about? its around where her urethra would be. somewhere in the middle below the clitoral hood