Dude, I wish I had your problem. I just finished school and got an internship right after... I miss school... it's the first time I haven't been in school since I was 4 and now that I am out, I want to go back (and probably will in January). Getting a job made me realize even more what I want to be ... a professional student!
My suggestion: get a crappy job, realize how good it was to be in school and how much you need school so you aren't stuck in a ****ty job, and that will probably motivate you. Since you got unmotivated after the Summer, coming back after travelling might have the same effect. But travelling can be such a growing experience, especially if you go by yourself, it really helps you find out who you are - and what your priorities are. It gives you time to clear your head.
I am going to suggest Amsterdam.
