I believe it is because you are doing a clear:both on your avatar and sidebar divs.
What might be better wrapping your content simliar to this.
Your avatar and sidebar would go here
All your other content would go here.
Where you have the content in a container.
have class left floated left with a specific width
have class right floated right with a specific width.
And this should fix your problem.
I think the only other way would be by not clearing both on avatar and sidebar,
Let me know if this helps at all.