A couple of weeks ago I found an interesting paper (PDF here) relating low levels of blood folic acid to poor response to antidepressants. Given that hoping-to-be and actually-pregnant women are encouraged to take daily 400μg supplements of folic acid, it seemed to me that little harm could occur if I were to try doing so myself. And yes, before you ask, I did do my background reading :)
I started last week, one pill at bedtime. I'm not discounting placebo effects, but it does seem so far that my sleep quality has improved dramatically. I'm now generally falling asleep three or four hours earlier than before, and sleeping much more deeply, waking after eight hours or so actually feeling refreshed and ready to tackle the day ahead. As to mood, well, again there's the placebo possibility, but I'd say that I'm more optimistic in general, and have more energy. I'd say it was comparable to the improvement I felt a month or so after I'd started on Venlafaxine.
Boots sell a pack of 56 own-brand 400μg folic acid tablets for a couple of quid. You may seriously want to consider giving it a try.
optimistic