Motivatie

** "Onthouden" in Dutch, does not have the same meaning as "to memorize". It means "to remember". That's why the sentence in Dutch doesn't really work. You could make it: "Soms hou ik ervan om nieuwe woorden te leren." Or you could say "Soms hou ik ervan om nieuwe woorden uit het hoofd te leren." 
You can use "onthouden" like this: "Ik herhaal nieuwe woorden tien keer in de hoop om ze daarna te onthouden."
*** This doesn't work in Dutch and would also not work in English. :) Sometimes I can't wait to study Dutch and sometimes not.
A better way to say it is: "Soms kan ik niet wachten om Nederlands te studeren en soms heb ik er totaal geen zin in." (and sometimes I totally don't feel like it).
**** In this context I wouldn't really use "opgewonden". It's better to use something like "zin hebben". So you can say the sentence like this: "In het algemeen heb ik veel zin om te leren, maar de laatste tijd niet (echt)."

Hi Fletcher! You have some work to do, but you're definitely going in the right direction. :) I was able to understand what you were trying to say. I'm writing to you in English, because you have your Dutch level set at A1, beginner. Please let me know if you prefer me to write in Dutch.