Lump On My Vulva

So I've been having super heavy periods and I went to change my tampon there's a lump on my vulva near my vaginal opening On the inside of my labia majora. It's swollen and hurts a lot and is quite large but is the same color as the rest of my vulva. I have never received any form of sexual intercourse but have performed on my female partner who is STI free (in addition to me being her first). So if it's not an STI???