What Am I doing wrong?

I love being a mom, but often I wonder if I am really doing a good job or not. I try to play games with them, read to them, teach them how to work, teach them how to respect, obey etc. And, I try to do it in a loving way. Then, why doesn't it work? We have really been struggling with obedience lately, and I'm not so sure why. I don't want to be a nagging-yelling mom, but I feel like I am. I want my kids to remember how fun it was growing up, not that, "my mom was always yelling at me." I love my kids so much, and would not trade my job as a mother any day. I only hope that I am doing everything I can to prepare them for the future.