For me it started suddenly six months after my dentist recommended switching to Sensodyne, which does contain SLS (Sodium Lauryl Sulphate). Switching back to my long-time favorite herbal toothpaste (no SLS) solved the problem within a few days.

Of course I can't be sure if it was SLS or another ingredient in Sensodyne, but I am definitely not going to try another toothpaste for a while now!