Try modafinil, or if you have too much cash lying around, armodafinil. Perhaps there are now illegal generics of the latter that can be purchased online for a reasonable price, but as far as I remember the differences are only in efficacy, so just double dose on modafinil for the equivalent effect.
I'd suggest you hold off on methylphenidate and amphetamine until you've exhausted more modest alternatives, particularly if this is just standard fatigue rather than a neurological disorder.
More caffeine as some suggested is markedly stupid idea.