If "Clear" is written in Blue then you can tap it to delete any history that may be there, even if you may not be able to see it.
Once History is actually removed, "Clear" will turn gray.
Before clearing it though, and if you can't see your History, try closing the Safari App, and resetting the iPad.
Tap the Home button to go back to the home screen, then double tap it to bring up the multitasking screen. Swipe the Safari screenshot up and off the screen to close it.
Then hold down on the Home and power/sleep buttons at the same time until you see the Apple Logo. This will reboot the iPad. When the iPad restarts, try opening Safari again, and check if you can see your History.