Why do i have trouble accepting what i am capable of?

I have set very high standards for myself, in ways that hurt me. I have an obsession with perfection, and it haunts me day and night. My skin needs to be clear. My hair and clothes perfect and appropriate. Even, if i am simply sitting at a table or in a clroom, and the desks are not lined up well, it would drive me nuts. But most of all, my biggest problem is my grades. I am NEVER satisfied. I don't know what to do. I try so hard, but my best is never enough. I NEED to be perfect and its driving me INSANE! I can't deal with it anymore, its causing me illness, I find myself so upset with the a grade such as a 94 or even a 98. I'm a freshman and one of a handful of those who qualify for college level biology PSAT's, that I am taking in two weeks, and I'm still not happy with myself. SOmetimes I feel that their might be a factor such as the indifference of my mother, or the pressure put on me by clmates who think I am perfect. Like I have to live up to their expectations. What do I do?