I've tried posting two books that are wish listed but I do not see a pending request at all. I tried to repost and then it shows I cannot post it because it's "already on my self." I posted one book successfully, but the next two will not post. Any ideas?  Thank you!

ahhh, I bet you previously received those books thru PBS.  When you receive a book, they 'put it on your shelf on hold'.  So look on your shelf with 'all books' selected (if it says 'posted books' those other books will not show up). find the book you want to post, make sure the ISBN is the same, then click the little box next to the title and click 'post'. 

FYI-- and yes, they won't let you post 2 copies of same book on your shelf til one is accepted for mailing out.

Hope this helps.