Bathroom Ventillation

[Jimbo]

My wife's really getting on my case about this so I gotta ask if anyone can give me some advice. I have a house that's not even 5 years old. In it I have a powder room that continually smells like the men's room at the Vince Lombardi Rest Area on the NJ Tpke at Friday rush hour. I don't think it's a case of anyone missing the mark and the bowl is definitely no leaking or anything like that. I suspect maybe it wasn't properly vented; the builder and his contractors were worth s%&*. I was pretty sure sinks and toilets are supposed to be vented by those small black pipes that come out the roof (as you can tell I'm not much of a construction guy which is why I need advice). There was a fan put in the cieling which vents out the side of the house, but by the location of this room there is no way a run straight up thru the roof could be made.
Is there a way I can check or who would be the best kind of professional I could call to come take a look? There could be a book of funny fishing stories on its way to you if you solve my problem.