Hi there Young lady.
I read your detailed history & note that you & your boyfriend were virginal & there is no fear or risk of an STD
While i wish you the best, this need not be entirely true. STD's like a viral wart
can still be spread through auto-inoculation with hand to genital contact & being a virgin does not preclude one from contracting or passing on an STD.
There are many glands in & around the vaginal opening & any of these could be inflamed & may or may not be secondararily inflamed leading to this swelling.
Perhaps a Sitz bath using a shallow tub with lukewarm water & a course of an antibiotic & an anti-inflammatory agent eg ibuprofen
taken in a 3 times a day dosage with food may help allievate your symptoms but dare say it will require a prescription.
Good Luck & Do keep me in the loop how you fare...but please remember while i do not have the right to question your sexuality or indulgence therof, i find myself duty-bound to advice you to practice safe sex
even if it is with your boyfriend! Cheers.