I haven't been seeing any Facebook posts for the last few days and I know my friends have been posting. What should I do?
I think you have made some changes in your news feed. If you did not do anything then please try to login to your account from another system and see if you face the same problem. Try to clear the cache of your current browser or use another browser or check with other browser and see if it solves your problem.
If not, click on down arrow 'v' at the top right of your profile and set News Feed Preferences.
From the left hand side under Favorites you can change your News Feed. It has two options Top Stories and Most Recent. Choose Most Recent and refresh the page. Check if you are able to see the updates of your friends on your feed.
Facebook does have it own way of sorting post. It will display post that are most interacted with (by likes/comment/share) and show it to more "friend". It is the same with all the content a page you follow post. you won't see all of it.
If you want to be sure to see all the post someone post you can put the in your "Close friend" group so you will be notify at every post.