A screen shot would help people see what is not correct. Did you make a new Post or update one when the problem started? Does the same formatting issue happen if you go to older past Posts or Pages that list earlier Posts?
Sometimes an error with the html can cause problems when a Post is edited.
I have seen some threads where the problem was corrected by.
Settings >> Writing >> Check "WordPress should correct invalidly nested XHTML automatically" and make a change to recent Posts and then saving the Post - they worked back from the most recent Post to the one that had an html error in it.