Did you know there is a spam filter on Facebook Pages? This is important to know because if you have a Facebook Page to promote your book you may not be seeing all of your wall posts from your friends. To see if you have any hidden posts, check the menu on the left sidebar:
There is a question mark in the Hidden Posts header that gives more information about this (see below). You can unhide any posts that are not spam, which you will want to do if people are engaging in your Page and being filtered out by mistake.