I thought exercise was supposed to be good for you

I am completely laid up on the couch, lying motionless on my stomach, heating pad on my back, typing one-handed because I pulled a muscle in my lower back earlier today. That's what I get for excercising. After my walk (yes, I said walk) on the treadmill, I was about to get in the shower and was putting on some music. I leaned over slightly for, I guess, a moment too long and I could hear and feel the muscle pop. This was immediately followed by pain, which has only grown as the evening has worn on. This is not fun. This is the fourth time I have done this in the last four years. I think it is becoming a tradition. So, I am trying to heat it up enough that I will be able to function for school tomorrow. Anyone got any suggestions other than a heating pad and icy hot, which are both already being utilized?