You shouldn't need to add
<br class="clear" /> over and over again to get it to stretch. All that's doing is adding line breaks, and you'll have to do it every time.
I'm looking at your source code, and one p[roblem is a HUGE error - you've got *several* anchor links that aren't closed:
<a href="http://think-theory.com/category/games-theory/" <img src="http://www.think-the
See that "a" part? It's not even closed before the image. It should be:
<a href="http://think-theory.com/category/games-theory/"> <img src="http://www.think-the
I've played with your stylesheet, and I'm guessing that you're using the visual rich editor. Your stuff is within
tags, and you can't see those when you're writing a post. If you go into the "code" area, add
class="left" to the
tag around the image. Also, remove the "max-width:100%" from the
img in your stylesheet.