Saddle issues

[Road Viexn]

Ok I have been logging some good miles on my bike and everything feels good until I am done with my ride. I am not sure if it is how I am sitting on my saddle or my saddle it's self. I get off and I am so sore right on my tail bone, right where my crack starts to be exact. I am sore for a few hours to a day after my ride depending on the length of my ride. I am fine when I am standing, but when I sit down I am so sore. What could be causing me this pain?

[Trek420]

Saddle is too narrow, stressing your sacro-tuberous ligament, which causes rebound pain when you are OFF the bike.