Using URL in the body of the Post

hi,
my site is http://www.bergain.co.uk/
I can post general post in my site but I can do anything link in the body of my post such as
GetDiscountCodes.co.uk
Everytinme I try to do something like this, it comes out and doesn’t save my post not even in unpublished.
Please help me here.
Regards’
Maz from http://Www.Bergain.co.uk