Because it would take a very long time for the page to load if you had to wait for ever posted by the friends and Pages you follow, Facebook only loads some of the posts that make up your News Feed to make the page load faster. Do not despair if you can't find the older posts, however. They are still available, and can be accessed quickly and easily, with just a few touches of your mouse.
Sign in to Facebook with the email address and password associated with your account.
Scroll all the way to the bottom of your News Feed page.
Click the "Older Posts" link located on the right side of the blue bar at the bottom of your News Feed.