What was the ambient temp during fermentation and did you use any sort of temp control? Hefeweizen yeast has a VERY specific smell. Not really very good either.
I recommend fermenting in the low to mid 60s (internal temp), and only for about 10 days before bottling/kegging. Hefeweizen doesn't need 19 days, in fact it's sorta counterproductive. You don't want that style of beer to clarify, the yeast is what gives it the flavor.
Scrape a clump of the yeast off the side of the fermenter and smell it, is that what you are smelling? (assuming you haven't cleaned it which you probably have)