Still after 3 years I'm left wondering if Google Panda hit me. Please look at the following graphs and tell me what you think? In the graph below you can see I have very predictable patterns due to my site being education based. The first mountain in each set is fall, the slight dip is thanksgiving, the big dip is xmas and then it recovers for spring season. As you can see in the 2012 circled in red, there was a larger than normal dip for thanksgiving and xmas. Panda 22 hit on Nov 21st and there was an undisclosed update on the 17th. Neither dip exactly corresponds. What is most troubling is that the spring mountain doesn't recover. Every other year it recovers. Even in 2014. It also has a big longer downward summer tail.
Relying on the past effect of the changes in algorithms in terms of analysis will be useful but focusing on the present that will invest for the future is the best method to stay in the competition.
Form the given graph, it shows that you are indeed hit by an algorithmic penalty. You can see that your site gets a little recovery due to Jan 22, 2013 Panda Update.
This site again? Check out my previous posts. This site has been used for spam, that's one of the reasons you're having a hard time with Google. There may be other reasons, but as soon as I saw the site was used for spam there was no points checking anything else.