What Causes Itchy Swollen Vaginal Labia?

Hi i have a quick question...I just got home and my vagina started itching really bad...so of course i rubbed and scratched thru my shorts and just happened to go look at it and notice my Labia Minora is swelled extremely huge...never had this happen to me...and the last time i had sex was 3 days ago so im not so sure that it has anything to do with sex even tho it possibly could...please tell me what i need to do....im 21