tedster - 1:49 am on May 12, 2013 (gmt 0)
Hello mamiakimo, and welcome to the forums.
This kind of month-by-month decline is pretty common these days, but from your dates and the record we have of Panda updates (see [webmasterworld.com...] ), it doesn't really look like you are suffering from Panda but other kinds of algorithm changes. There's a lot of this going around, too - and it can be pretty hard to diagnose and fix.
I hope our forum discussions here can help focus you on many possibilities. We have members who have long experience. Though SEO has become much different these days, with a much stronger focus on user experience, we haven't given up at allon imprvoing our lost rankings - at least not most of us ;)