I had a hard time finding my Sent messages, too. If you click on "Private Messages" in the box in the upper right corner of the screen (under the "Search" box). It should take you to where it says "
Private Messages in Folder: Inbox
" If you click on the triangle next to "Inbox" it should show "Inbox" and "Sent Items." Click on "Sent Items" and it should show what you have sent.
There is another way to find "Sent Items" when you click on "User CP" (on left side of screen) and it is similar in that you have to click on the triangle to the right of "Private Messages" and it will say "Folders" (not clickable), "Inbox" and "Sent Items."
Hope this helps.
Janey - Neat people never make the exciting discoveries I do.