I tried modafinil a few times. I was never diagnosed with ADHD but I was describing to a friend basically exactly what OP said, mixed in with a lack of focus @ work. He suggested I try modafinil and gave me a bunch of his stash (along with some stronger things I wasn't as keen on). Taking some before I hopped on the tram meant it had started to take effect around the time I sat down and started work, and I felt remarkably more motivated and focussed during the following ~8 hours or so. It's a bit of a game-changer. I felt a little bit like the day whizzed past, and had a bit of trouble sleeping afterwards so I was sure never to use it more than a couple of days out of any given week.

I think it's of questionable legality here, but if you can get a doctor to prescribe it legally it's well worth looking into.