Happens. Often. Get some Savlon or Vaseline on the area, often. Don't wait until it's sore. Get the product deep into the fissure, I've had this with lips, heels and end of fingers and found that keeping the areas moist helps healing. Or put some of the Vagifem there too. Often is the trick!
Particularly after going to the loo ;-)
Nowt is taboo on here !