The problem is located in the code. Open the link bellow
http://www.nikost.gr/blog/index.php?start=141&length=3

And you will see that the sidebar appears normaly but you will notice that the text doesn’t appear. If you open the link bellow
http://www.nikost.gr/blog/index.php?start=144&length=3

You will notice that the text appears underneath and not at the side as it should be.
The potation problem appears to be in the table text so it doesn’t take over the space of the sidebar

I would recommend the following choices

In the built of the blog to exist the option clicking on the ‘’category’’ to list it in category.
Also the ability to store separately the whole blog if someone wants to use it to built another page
And the ability to insert between two posts a google advertisement