You said he was scraping along the rocks?
If your sick Betta fish is scraping up against plants and other objects in the tank, it is quite possible that he or she has contracted a parasite. Parasites can be anything from Ich, or white spot disease, to worms that hang off of your Betta fish's body. Parasites can be treated with medicines such as Jungles Parasite Guard, Nox Ich, or Malachite Green. Make certain you are positive what parasite is affecting your fish before you dose the tank with the chemicals.

Also was he hold his fins to his side most of the time? Not moving them?