Its probably a reaction to the type of condomn used or maybe if the sex was rough, then that could be a result. Either way, i dont think you should be worried about it, but if the swelling doesnt go down neither the pain, (give it atleast 10days from day of first signs), you can go and see your gp.
That exact thing happened to me once. I never did find out exactly what caused it but I thought it had been an allergic reaction to the type of condoms we were using. My swelling went away in a day.