TheOptimizationIdiot - 2:28 am on Apr 18, 2013 (gmt 0)
I found the google can index 3-4 pages per 3 days or one week.
This sounds like you're not getting crawled very much or may have a structural issue if that's all the pages you can get indexed in a day or week. I'm working on some "decent sized" sites and have had 1500 new pages indexed in a day recently.
Have you made changes to the site before or after the ranking change?