Are all the items from the same seller?
Unlike other sites, eBay has literally millions of sellers using the same site.
Check that your Paypal account says that the other four items are marked paid.
Then contact each of the other sellers, with the eBay transaction number and the Paypal payment number, and ask for the shipping date, the service used and the tracking numbers.
Don't worry if there are no tracking numbers, these benefit the seller not you.
If you don't get a satisfactory answer, go to the bottom of this page and open Disputes (Item Not Received). There may be a short delay before you are allowed to open the disputes.