Where and how deep was the cut?

If it was just torn a little, that's actually really normal to happen during sex. Little tears can happen inside the vagina from rough sex or from fingernails or other things.

I guess if you're really worried about it getting infected, and it's outside, not inside your body, you can wash it up with some antibacterial soap and cover it.

If it's inside, I wouldn't worry. I mean, if you cut the inside of your mouth, you just let it heal, right? You don't worry about your mouth getting infected... and your mouth is dirty dirty!!!

The genitals actually heal very quickly.
Just take a easy wiping the area after urination and defecation so that no feces gets near the area. Feces is full of bacteria and if it comes in contact with the cut and not properly cleaned off than there is a chance that the cut could become infected than you would have a much worse problem.
I suggest after you go to the bathroom and wiped and all that you should clean up with a baby wipe to be sure that it is extra clean.

i have small lumps on the outside of my vagina and it looks infected what can i do?