Levoxyl and cancer surgery

I would like to know if anyone is experiencing or has experienced the following side effects:
I am 28 yrs. old and have been on levothyroxine since April 2004. I started graduate school immediately following my body scan and RAI treatment(5 days after when I was no longer radioactive) in August 2004.
After immersing myself in classes and field placement, I found myself having difficulty concentrating on my work and I had little to no motivation to get out of bed to go to class. My grades dropped and that made me even less motivated to continue on with school.
I went to my dr. and after telling him about my side effects: lack of motivation, difficulty concentrating, emotional instability, he just said that he does not believe that it is from the meds.
I have dropped out of school for the time being because I just can't get enough energy to go every day.
Has anyone ever experienced these symptoms? If so, do you believe they are an effect of the meds. or having gone through cancer , surgery, etc.?
Feel free to email me. I'd like to get some feedback. Thanks.
Amy ******