Change your oil.
Coconut oil is very strong. Perhaps you need to start out with something not quite as heavy, like Sesame or Sunflower?
As far as the cracks, yes we have talked about that before, many moons ago. Usually it's because the rest of your teeth are getting cleaner and now you are noticing the deep crevices.
With the right oil this should go away.
*edit* by the way, your teeth should feel really clean after pulling and rinsing.