Hello. Thank you for posting.
There might be a few reasons this can happen. The vaginal area tends to get swollen and wet when you are aroused, and that swelling might persist even after sex is over. Sometimes the simple friction of sexual activity can lead to swelling in that area and will often go away soon after sex. If you are still swollen hours or even days later, this might be an indication that the sex was too rough or you weren’t lubricated enough. A pH balance in the vagina that is easily changed, even by the act of sex can lead to infections and other problems that cause your vaginal area to swell. If you have a history of getting yeast infections or urinary tract infections after sex, this might be the problem. If you are concerned, see your GYN.