Please help me. I don't know what kind of mental illness this is? Help!?

Okay. This is about my mom. I shouldn't put this out here but I need to know what illness this is. We tried the doctors but nada, they just tell us "Mental illness". They have not helped at all, they said nothing. My mom is 35 now and she does many things that don't make sense. If you tell her something she does the opposite. My mom has always been like that, and this time shes really making me go nuts.I think she has some kind of depression and mental illness. When she gets in trouble she won't look at you in the eye. She shifts her eyes. She done so many things that doesn't make sense. I think she even enjoys it when people get mad at her. Maybe because she gets attention? Even my grandma told me something of what she did when she was little. She told me that when she was little she hid behind hangers in the shopping store, and my grandma said she was looking for her and she popped out saying "Hehe you didn't see me!" and she was laughing while being scolded. She did something so similar just so recently. All of a sudden she disapeared and I was scared. I looked everywhere in the house. 20 minutes. After ten minutes i gave up and thought she took a walk. Me and my grandma were worried for 20 minutes. Then all of a sudden she pops out of her closet laughing and saying "Haha you couldn't find me" and we were yelling at her and she had a smile across her face. And she is insecure about her weight and unfortunatley me. She gained weight and she might have a weight disorder. I know that before she used to have bulimia. But shes really short [ 4"9 ] and shes 91 and it doesnt sound much but she looks big for her size.She complains about it and eats more and more and more. Shes insecure about me. Im at my families house and she calls me and says the same thing over and over again to keep me on the line. Please. If you know ANY of these please. HELP!