RogerThat - Search engine rankings are competitive, like a horse race. There are some 200 or more ranking factors, and they change over time. There's a general understanding that Google changes its algorithm 500 or 600 times a year.
Beyond algorithm changes, your rankings might drop because your competitors are making improvements to their sites, perhaps more than you've been making to yours. The best sites are perhaps attracting more and better links over time, which would change their position relative to yours. Some ranking factors are also time dependent.
The reasons the results might change are what this entire forum is about. Your questions suggest that you may not be understanding this.
The end of the honeymoon period, as aakk9999 explained, is a common reason for a new site to drop. If a site hasn't attracted traffic resulting in high quality links during that time, it will generally lose position.
BUT when I search a long tail keyword (3 words when the main keyword is 2 words) my website appears, as I said, at the very first result.
Longer queries are more specific, and as such are less competitive than shorter, more general queries. And different queries have different degrees of ranking difficulty.
It is very strange to me and it seems like Google just removed my website for this specific query !
Just because a page isn't ranking where it used to rank does not mean that it's been "removed", though that can happen.
Using the site: search with a specific query is one way of checking whether the site is in the index. Searching for a unique phrase on the page in quotes is another.
As minnapple suggests, pages will sometimes drop out for days or a week at a time. Perhaps someone duplicated your content. I think you've got a lot of reading to do to catch up on the basics. You might consider posting in our
New To Web Development forum [
webmasterworld.com...] for more detailed answers on basic questions.
