all-in-one seo / any other seo plugins i should use with all in one? / google si

hi guys
apologies upfront if this has been posted in wrong forum area. I don’t even know if its a plug in issue. since I moved to www.ads-software.com I started using yoast’s seo plug in then I moved over to all-in-one everything has been great better than expected. when I started using the plug-in i was averaging under 1000 visitors a day but amazingly that grew to 1,500, then 2000 and sometimes rising to 2,500plus but suddenly over a 5 day period ive suddenly dropped to to under 1000. Ok i do get bad days but usually thats about 150-300 not 2,500 to under 1000 in 5days. Ive been following the same things i do to promote every day, but somehow its now going downhill is it just me or possibly something interfering with the widget? i have the odd day or two lower visits however Ive never had as big of drops so long periods. if its myself is there any other plug ins i can use to help boost the visitors?
I’m also looking at google sitemaps however im totally lost on the jargon havent got a clue how to install, configure it properly

paul