I would certainly expect some response to Levodopa (which is the active ingredient in Madopar and Sinemet).
You don't say what dose you are taking, maybe its too small. But if you genuinely have zero response to Madopar I would question the diagnosis. I've heard it said that a response to Levodopa is a symptom of what's called idiopathic (=regular) Parkinson's Disease.
So my conclusion is that either you need to increase the dose or maybe you have some other form of Parkinsonism. Either way I would push for an earlier meeting with the consultant.
Not reassuring, I'm afraid, but I would say if you don't see an initial response to a PD drug within one month, you need to start asking questions.
PS I was diagnosed in early 2012 and now take Madopar and Mirapexin CR.