Swollen vagina is always a sign of a yeast infection. Yeast infection is caused by a fungus called "Candida albicans" which is normally found in small amounts in the vigina. This infection is often found on people with weakened immune system, in most cases it is not the sex activities which bring women yeast infections.
Women with yeast infection may develop symptoms including:
Pain/itch/burning at vulva area
Pain/itch/burning in vagina
Pain during intercourse and/or urination
Cottage cheese like vaginal discharge
Yeast infection is not something serious in most cases, but lots of women are bothered by recurrent infection and can't find their way out. You should see a doctor and get prescriptions to avoid a worse condition. There's a herbal medicine named . Pill also works well, you can google it and have a look. Hope you can get rid of your ailment soon