I'm always confused, I'm either constantly daydreaming or sleeping, I can't read a book without compulsively opening up several others and end up totally lost and depressed. I need help, someone?

My dad tells me that I’m a smart girl and I’m capable of handling anything and any situation. When I mentioned to him that I could be suffering from A.D.D, he said that I and nobody else can make me concentrate. He keeps reassuring me that it’s all up to me to make something of myself and handle my life. I’m twenty-one and I’ve a younger brother and he’s successful and smart, while I’m just known as the kid in the house. I won’t give up on myself but the worst part is self-pity is setting in and I feel that’s going to really wreck me.