What Causes Swelling And Itching In Labia Minora?

Hi, I my right labia minora is swollen a bit. Not huge, but significant. I haven't had sexual intercourse in over two months. This happened a couple months ago before I had sex but it went away after about 2 days. It's back again now with the same symptoms/characteristics (swelling, itching, tender,). I masturbate if that attributes to the cause. What could this be?