well i've never brewed a lager, but its my understanding that 3 weeks in primary is normal. cooler temps = slower metabolizing of sugar by the yeast.
you might want to gently swirl the fermenter (no splashing) just to circulate the yeast a bit.
maybe triple check your thermometer in case its reading warmer than it really is.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10