Hi,
Welcome to the ehealthforum and thanks for posting on it. Labial swelling can be due to many reasons like infection and inflammation of the vagina causing vaginitis, allergic reaction because of using tampons, sanitary pads and latex condoms, bacterial vaginosis, trichomoniasis ( less likely as you are not sexually active), changes in vaginal environment within the vagina due to frequent vaginal douches and trauma to vagina or labia.
Apply warm compresses and wear cotton undergarments. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen are also helpful. But they should be used only after consulting your doctor.
I hope it helps. Take care and regards.