It's just asking for attention! Go to the icon that looks like a little pacman dude yelling, and hit timeout. it should look like it's crying. if it does, you've solved your problem! if it jumps up and down and makes a mad face...you're on your own. sorry. :P
Maybe it's because you played games too many times in a row. But when my tama didn't wanna play games, it was because it was underweight. It was an adult and only 17 lbs! :P
I brought my tama to school once, and so I kept in it my jeans. I forgot it was in there, and my mum washed my tamagotchi! It still worked, but the battery never lasted as long. Also, the background looked wrinkly and that sorta freaked me out :P