URL repeating in blog posts

Hi all,

First time to the forums – hoping you can help! I recently began a wordpress site and am loving it. One little niggling thing though – when I create a new blog post, my permalink comes out as:

http://sitename.com/http:/sitename.com/test

repeating my URL. Now I want to have it so that when I create a portfolio page, or an about page it comes up as:

http://sitename.com/about

but for blog posts, repeating the URL obviously looks a little strange – any thoughts, advice? Am I missing something very simple

Much appreciated!
Jon