A lot of people can't find apps in the purchase history on their iPhone/iPad. Incidentally, you'll find the apps when you access them via iTunes on PC/Mac but when you open the purchase history on the App Store, nothing shows up. Is this a problem you are facing?
First off, don't worry because thousands of users face this issue. It's a well-known issue.
There is no one-particular-fix that solves the problem but you can try a lot many things to try and fix the problem.
1. Wifi over 3G: It's a known issue that the apps in the Purchased section of the App Store load slowly if you're on iOS 6.x. Apple changed the App Store code to act as an HTML app. So, the first thing you should try (or make sure) is that you're using hi-speed, stable Wi-fi.
Also, it is also sometimes generally accepted that if you've downloaded a lot of apps, the load time will be slow even over hi-speed Wi-fi. However, if you're on Wifi and still can't see purchased apps, let's try the next step.
2. Sign-out and Sign-in
- In the App Store, scroll down to the bottom (on Featured tab).
- Now, tap on your account. Log out of it.
- Re-login into the App Store using your Apple ID.
- Check the Purchased section (via Updates) to see if the downloaded apps show up.
This solution is known to work somewhat successfully. Problem with caches or something.
Did this method fail to work?
3. Sign-out of iCloud and Sign-in: After iCloud sync and backup, things have gotten a little complicated (not for the users) as to how apps are managed. In rare cases, signing out of iCloud as helped restore the apps on the Purchased section in App Store. I really don't know why or how this fix works but you can try this.
You can sign out and sign into iCloud through Settings → iCloud
4. Last Call: Use the Search or Use iTunes: If nothing works, you'll just have to use the search function to find that purchased app that you're looking to download again. Alternatively, if you're not comfortable with this, you can just open iTunes on your PC and log into your Apple ID account.
Then, it's just a matter of clicking on the Apps tab from the sidebar. This will show all the apps that you've installed.
In the extreme case where you absolutely need the purchased app history, you might resort to restoring your iPhone/iPad (either through a backup or set up as new). You can login to your Apple ID in the App Store and you should be able to see the apps in the Purchased section.