SEO changes violently?

[Crazy_Teacher]

OK Interwebz, try this one. I work on the SEO for my company which has two domain names. Last Friday I was thrilled when I saw one of them had jumped from page four of Google to fourth place on page 1. All my work had finally paid off. Or had it?

Monday I was gutted to see all of them had disappeared and the other domain name was the only one to show up, but back on page 4.

Now it's Friday again and it is déjà vu! I woke up this morning to find the first domain name back up at page 1. What am I doing right/wrong?
@Josh: When I got to work the website was a mess. I cleaned up the description, added titles to the web pages (yes, they had no titles), reduced meta tags to under 500 characters. I have translated the site into 3 languages, added Web 2.0 (FB, Twitter, Flickr, SU, YouTube) with updates on those sites once a day to once a week. I have started making weekly press releases. I have gotten rid of all of the <H5> and made headers <H1> again, changed a lot of the text, and so on. Things like that. I will be curious to see if you think those are effective or just common sense...