What Causes Swollen Labia Minora With Itchiness ?

I am 15 years old and when I go pee after I go it s kinda painful and then tonight I have been itching down there and my left labia minora is inflamed and is kinda red and it really hurts .. I am not a virgin I had sex 2 times but only one was protected and the last one I had was not and I do not have an STD because he has been tested . what is going on