My site and keywords

I have put up a few sites over the years but my favorite site is my travel site. By the time I put this site up I thought I kind of had and idea of what SEO was about and after about 6 months after putting up this site I was on page one position one on Google.

It stayed there for almost a year but didn't get many sales from it probably because I thought going for a non competitive keyword would get me there faster and it did. However over the years I have changed the look of the site a lot but never really did anything with my main keywords but over the last couple years the big booking sites have taken over the top 10 positions I use for my main keywords.

I have stayed on like the middle of page 2 for a long time then towards the end of last year it went to page 3 which is where is was till a couple of weeks ago. Checking yesterday I found it on page 14 and couldn't really believe it. However when checking google analytics I saw a couple keywords that they said people typed in to find my home page which is the page I had my home page on for so long. So I plugged it into to google search and I found my home page on page on in position 6 or 7. Which was puzzling because those keywords are not used anywhere on any page of my site and my main keywords that I have used for years are in not everywhere but about what they should be. The funny thing is the keywords I have been using Google says only gets about 100 uses a month where the ones I don't have on the site that I am on page one for gets thousands. So after this long story my question is how in the world am I getting rankings for keywords I don't even use and the ones I use have all of a sudden dropped me back to page 14.