I need help..

It's Sam again.
So my mom and I just keep bumping heads about everything. I wanna tell her how depressed I am so I can go to a therapist, but I know she would get mad because when I told her I have no self esteem she bitched at me. Am I really that bad of a person? She also always compares me to my brother. He is a perfect, angel. What am I? A fucked- up child, and my mom always tells me I was a mistake. They weren't suppose to have me.
Do you guys have any ideas on how to tell my mom I'm Depressed without her getting pissy with me?