Why is my labia minora/vagina area swelling?

Hey, well last night, when i was about to go to sleep I noticed my vaginal region itching, then all of a sudden i believe it was my labia minora that became very swollen but it was only on the left side. The last time i had sex was three days ago, and I used protection, but he went in without a condom but I made him stop; However, I just started on YAZ birth control a week and two days ago, and I have heard that could be why.But as the day went on today the majority of the swelling went away, but still a little bit of itching and rawness. What could be going on? And what could be the cause of it?