I have a "knot" on my lady parts....

I was taking a shower and cleaning myself when I noticed that one side of my vagina was swollen a little and sore. Like where my hole is. On the side of the "hole" I feel a knot. And its swollen. I thought it might be just a pimple that might be trying to form or something like that but this has gotten bigger over the last hour and its really swollen around and above the knot. What could it be??