I thought levodopa was a prescription-only medication? Maybe not.

This might strike you as an off-kilter question - but have you considered going off of the stimulant? Or perhaps you could switch to modafinil or something more mild? I am on modafinil and it helps me a lot. I don't really get tired. (Except when I should get tired).

Postscript: I don't know how stimulants work.