Slight amount of swelling in vaginal lips is normal due to trauma after intercourse.
You can try sitz bath (sit in tub of warm water for 15 mins) and take anti inflammatory like ibuprofen
If your pain and swelling does not reduce after 24 hours then you need to take it seriously.
It will not be just due to recent intercourse.
Also if your swelling is increasing and spreading to the mons (triangular area) then you need to visit a gynecologist to rule out possibility of abscess
. This is not directly related to having intercourse but can be coincidental. If you have recently shaved or use any irritant creams causing folliculitis
(infection of hair follicle) then it can lead to swelling, redness
If you get fever
, then possibility of infection and abscess further increases.