That's happened to me once but it has never lasted as long... Maybe its some sort of infection. A yeast infection maybe? It doesn't have to be sexually transmitted and if the itching doesn't stop, its definetly some sort of yeast trying to develop. Get it checked out before it gets any worse.

The exact same thing happened to me after sex. And im std free! I got the swelling, not just on my lips but the opening of my vagina and up around my clit too. I dont know what it was but I did all the stuff i'd usually do for cystitis just to try and make it go away! Drank lots of cranberry juice, and took a teaspoon of baking soda in water (lowers acidity level of urine). I also put a bit of plain bio yogurt in and around my vagina - the cultures help fight yeast infections, just in case. It stayed for maybe a week and then settled down. I was on my period too. I dont know if it's related.

Wash down there normally, but extremely gently. I found using soap and stuff directly on the swollen area made it worse, so if you need to, wash around it and just use water on the swollen bits for a couple of days. Avoid sex, and dont touch the area cos you'll only make it worse and risk introducing infection. If it doesnt go away, or if you start getting other symptoms, see a doctor, you may have thrush or another infection.