The symptoms you are telling resembles vaginitis
. Again same can occur in case of trauma.
Vaginitis can occur either because of bacteria/ virus/yeast infection.
But in that case you will get vaginal discharge
also along with abdominal pain
Treatment will vary based on etiology- either antibiotics/anti-fungal medications.
As the area is red, swollen; it requires local examination for correct diagnosis. So consult gynecologist.