I cut my vagina by accident , and now it stings when i pee what can i do? can this cause an infection?

Apply antibiotic: Treat that area like you would with any other cut. Keep it clean with soap and apply antibiotic cream till it's healed.

Cut vagina: I assume you don't need stitches. Soak in warm water and apply dome burrows solution (buy at the drugstore-mix packet in water and sit in it or apply compress-wise). It should heal quickly. A topical antibiotic like neosporin in good too.