Again, great milestone 100K
It looks like June-Aug was your anomaly, go into webmaster tools and take a look at your pages report with Feb - May compared to Aug - Oct, and see which pages lost traffic, then go back and re-work them
You caught a nice chunk of traffic around July, did your checks go up during that time period ? If so need to also look at the pages report for Jun-Aug and see which pages those were, make sure they are still in place.
I would think with a site based on models that are online, if a model dropped off the site, that might be where your traffic went
Good Luck!