It could be a lot of different things. If you give us the site address, folks here on the forums will take a brief look at it and see if they can spot anything right off the bat.
I always like creating test sites with specific known performance characteristics. For instance, I always create an html-only page. I also create a bog standard Wordpress one-click installation.
Being able to compare the performance of different pages - a static page, a simple dynamic page, and your full blown website, will help point to what the underlying problem really is.
Oh, and just to be sure - did you personally code your site or did you use off-the-shelf software of any kind?
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