MatBell
My experience with being happy or unhappy at work has been associated with the supervisor I had. The right boss makes all the difference in the word and a crappy one is just hell. When looking/interviewing for your next position, try to find a connection to your supervisor. Make a list of traits you like and dislike so you can ask probing questions about their management style and the company culture.
Good luck and know that going to a job you hate is just plain unhealthy so don't beat yourself up. You made a positive decision for you self improvement.