Over the last two years or so I was able to really cleanse myself of negative thinking by simply recognizing it's all relative. Quick story:
When I was younger, my mother's standards for how things should be done were always higher than mine. If she asked me to cut the grass, I'd cut the grass, but I wouldn't sweep the pavements of the freshly cut grass clippings, or whatever. My mom would always tell me to go back out and finish the job, and being a lazy teenager, I'd complain about how I was too tired. To prove a point, she'd go out and sweep everything in 30 seconds, and come back with a "Was that so hard?"
For a while it never really clicked with me, but I slowly started to realize that anytime I had to exert myself beyond what I had been anticipating, I'd always complain. In reality, what was being asked of me was often a thirty second task, and I just had some stupid mental block that led to my poor attitude. Now I'll go above and beyond what's expected of me, and I tend to be a lot happier after the fact.
It's through this sort of thinking that I was able to purge myself of bad thoughts. What happens is going to happen for whatever reason, and it's a lot easier to just deal with whatever has to be dealt with than to complain or worry about it. For me, that realization alone was enough to set me straight.
In your case, just recognize that you must take the classes, and complaining about it won't actually solve your problems. You're expending more effort by thinking negatively than simply going through the motions and going on vacation some other time.