Ugh, I know how you feel!
I don't clench my teeth, but I have three areas in my canines where the gum line is receding and some of the root is exposed and OMG is it ever painful!!!
My dentist said it's probably being aggravated by all the pregnancy hormones, because I didn't have this problem before, but he suggested that after the baby comes, that there is a surgery that he can do to make the gum line higher in those places and cover up the exposed root.
I take good care of my teeth too, and I'm only 27 years old, it's not like my teeth have had many years of abuse. I brush and floss like I'm supposed to but I always get cavities and my teeth break really easily :(