Surreybirder, you're getting eight hours sleep a night (I can only dream of that - well, actually I can't...) which makes me wonder if there's not something else going on that's making you tired. Have you had any blood tests done recently? Are you losing or gaining weight?
Apart from the fatigue and lack of concentration, do you have any other PD symptoms? Those two conditions alone seem to be an odd diagnosis of Parkinson's.
But to answer your original question, I've tried three PD meds so far, and they all (to varying degrees) stop me sleeping so I'm tired a lot of the time. My PD nurse suggested Sinemet (L-Dopa) to help with the energy levels, but even that's not helped.
Diet-wise, make sure you get enough protein and lots of fruit and veg. It'll make you feel better physically so might help combat the tiredness.