I've bought and installed both Dawnguard and Dragonborn, and have beat both DLC's. I was playing files with both DLC's still working around two days ago. Today I tried loading up one of my files that was a master vampire with vampire royal armor (dawnguard exclusive armor) and the character was naked, with the vanilla vampire statuses. The character was in a Dawnguard area, and the save file shows the armor and the Dawnguard location, but when loading up it puts my character in Riverwood Inn.

Checking on the Skyrim main menu it says no DLC's are installed, and when going into the XMB under game data there is nothing for Skyrim. I haven't deleted them. The only thing I've done since then is deactivate a ps3 account from this PS3, but that account has NO relation to Skyrim in any way (no saves, the DLC was bought on a different account).

I'm re-downloading them now and I hope everything should be working again, but I have NO idea why this happened.

do that and let us know what happend. Don't play around with many accounts, and see if your game code is exactly the same with your DLC you downloaded.