What Could The Itchy, Reddish Blister On Labia Minora Be?

I just went toilet and as i was wiping i felt something thats not usually there, i got a pocket mirror out and checked to find my lower left labia minora and its swollen about 4 times the normal size and looks like a very large blister but its not a blister its just really swollen, its uncomfortable to walk but no pain at all just really itchy and is red, i dont know how this came about in the last 2 hours from being perfectly normal, could you tell what it is or help me to get rid of the swelling?