Just finished HTML and CSS on Treehouse - What next?

Hi everyone! Basically I've just completed all of the Web Design tracks for HTML and CSS (Foundations & Layouts) and now I'm feeling a little lost as to where I should go from here. I've been making notes throughout my learning and recently attempted to design a responsive basic webpage using floats as my layout method.

I'm on Treehouse because I'd eventually like to create a startup site/project and so the dream is to make attractive, smart websites from scratch but I have to admit my current attempts with the float layout isn't perfect (though I'm just happy I managed to make a site that scales and adjusts between a mobile and desktop design!).

I'm just wondering if anyone has any advice on where to go from here? Do I spend a little time attempting to make yet another site with what I've learned, complete the rest of this Web Design course (which seems to now move across to other design elements besides coding) or do I start a Javascript/Wordpress track that will introduce Javascript into the mix?

I think I've begun to feel a little frustrated with my current limited abilities with basic HTML/CSS knowledge and so I want to apply some new exciting elements like graphic design or Javascript to make my websites come to life. What am I ultimately going to get out of following these different routes?

Thanks!