My daughter is 9 years old, up until she was 5 she was the sweetest girl. But then she started not listening or doing her little chores. Every year it got worse, she doesn't want to do any chores just playing or watching tv. She is constantly arguing with her sister (7) and they sometimes end up hitting each other. She ignores everything I say or ask and we are always arguing. She want everything her way, without thinking about the consequenses. When she doesn't get her way I get a mean look from her. What I don't understand, is she would be "normal" for a week or so, and would wake up grumpy one morning and we would be in for angry tantrums for a week or up to three weeks. She finds it hard to keep friends, because she's nice for some time, and then she's angry and mean again. She is very bright, I had her at a pshycologist, but to no avail. I tried everything, her diet, looking at her environment, what could upset her, doing different activities, nothing made a change. It makes it extra difficult when your one child is behaving and the other one is difficult. Could it be a medical problem?