I would guess that prednisone is at least partially responsible for your horrible mood swings. It's a great anti-inflammatory (works well for most everyone), but the side effects are wicked. Mood swings are definitely a side effect, also insomnia. You could always talk to your doctor to see if you can start on a dmard and gradually lose the prednisone. My rheumy calls it a bridge drug, and only prescribes it when a patient is switching from one dmard to another; it's more of a transition drug rather than a mainstay tx.
Hope you feel better soon,