Somebody please explain this SERP sorcery to me!

Autoblogs are driving me furious. Before, I tell you what really happened, here's a little background:

- I have a blog that almost 4 years old.
- It has a PR 3 and 15000+ baclinks
- It used to rank very well before November, but after that the rankings have just dropped (Panda perhaps?)
- Last time I posted regularly was 2 years ago, and ever since I had just been writing once a month or something.

Now, my rankings are shit, probably because I hadn't posted anything in the last 4 months. So, when I decide to post something three days ago, the post page is now indexed, yet an autoblog is out ranking me for the exact post search.

I'm coming to believe now that my website might be facing some sort of a penalty? For my main keyword, I used to rank 1st or 2nd, then my rankings fell to 5/6 in November and now I'm not even on the first page. Another issue might've been that I haven't done any backlinking all this while either.

So now, tell me please. Where do I begin? I'm planning on writing weekly now and how would you suggest to do the backlinking without raising any flags on Google. Knowing that I've done zero backlinking in the last 4-5 months. Things have changed still then, so please advise me.

Thanks in advance!

check your webmaster central account for a message from google to see if you've been hit

google likes fresh content and will crawl the site based on how frequently it has been updated

beyond anything huge that you've overlooked like a robot.txt that is blocking google, you should check the quality of your backlinks because google has recently hit many who had "over-optimized"

Yeah I guarantee you it's the back links quality.