You may actually have cultured a lager yeast without knowing it. Some breweries don't bottle-condition with the same yeast that they brew with; sometimes they use a more shelf-stable yeast (like a lager yeast) to bottle-condition their beers. I'm not sure if SN does this, but it seems possible based on the results you are getting. A hefeweizen yeast should be giving you a radically different profile (fruity or spicy depending on fermentation temperature). What temperature were you fermenting at? Also, try a taste of the beer and see if you are getting any of the classic hefe yeast character. If not, you may not have cultured a hefe yeast. Also, worst case scenario is you have an infection.
Hope this helps,