Something's not right. That should have fermented out by now. I've never had a lager under 1.050 take longer than 2 weeks to reach final gravity. It could be any of a number of things:
- Your temperature isn't really at 52°F and is really in the 30s°F
- Your yeast wasn't all it was cracked up to be... too small of starter, low yeast viability, yeast mix-up with an ale yeast, etc.
- Your hydrometer reading is wrong and it really is fermented down to final gravity
If you can rule all of those out, you'll just have to wait it out. Check it in a couple days and see where it is. Has it reached high krausen?