Mimi, another thought, your problem might be seat position ..... have you tried altering saddle angle and fore/aft position, etc?

Looking at the pic, I can't see how you adjust saddle height (I am exquisitely sensitive to the smallest change in saddle height - I get excruciating left sit bone pain if it drops by more than a few millimetres)

Also, that unsupported post looks like it would be quite "bouncy" and may be contributing to your comfort problems - do you notice much bounce when riding?