Hello,
This swelling can be due to a cyst or vaginal infection. Apply warm compresses and take some anti inflammatory pain killers like Ibuprofen/ Diclofenac. If the symptoms persist then get it evaluated from a gynecologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Could be as simple as a yeast infection or major like herpes which btw you don't need to have sexual intercourse to get. Get seen asap.