vaginal opening is swollen TMI

I've noticed lately that my vagina is swollen. it's only the opening not near my labia or clitorious. I've had occasionally burning but it's very mild and doesn't happen enough to be a yeast infection. along with that, Ive had slight pain for a few seconds when having sex with my fiancé. we have sex very often but I know I don't have any infections. period is due the 9th any advice please?