Sarah,
I too had extreme fatigue from Methrotrexate, Temodar, and Rituximab for CNS lymphoma and was presecribed 5mg of Ritalin. It was amazing and I would strongly encourage your husband to give it a try. I had no side effects and was able to function through a normal work day without having to nap (although I still took one at end of work day). I wish you good fortune in your ongoing battle.
Cheers