I go through cycles with this, and always have in any job I've ever worked.
The best cure for me is to change up my routine, to try and do something fun and different... like, maybe you could get permission to do an art project or make a book or something with the kids (or maybe you don't even need permission, you can just do it), or look for new games and activities. If you're a little bored with your teaching, chances are so are your students... like the saying, "If mom ain't happy, nobody's happy...", I think it is also true with teachers.
Also, sometimes I get tired of my social group... try and fine some new friends (and keep the old ones too!). Have you heard of Couchsurfing.com? Maybe there are people in your area who would like to hang out... I love couchsurfers and find a nice social group, and ever changing social group everywhere I go.
Lastly, I agree that it's good to complain and get things off your chest, but avoid overly negative people who are also burnt out because it just makes for a gripe fest every time you hang out. It's like sitting in the teacher's lounge in the states... I avoid it because everyone sits around and talks about all their problems and how much they hate their job... I find it's best to avoid it.
Korea doesn't give nice-long-refreshing vacations... I think good vacations do a lot for teacher quality, you need to refresh your self as much as the kids do, and vacations here are just long enough to make you dread coming back...
Good luck!