Precious ChickenFan, there are so many possible reasons for your mother's behavior and for your reaction and feelings toward that behavior. To list even a small part of them would take a long time. Seeking another trusted adult (such as a counselor) - as so many others suggested - is a really great idea.
Another piece of good advice is that you cannot change others, you can only change yourself and the way you respond to others. Determine to be the best you that you can be.
From the age of about 8 I had problems with my mother. I, too, spent most of my time in activities that took me away - mostly reading. Still, I showed respect to her, tried to get along, and never would have thought to sass her back.
I was determined not to parent the way my mother did and made a consistant effort to copy what I saw as good points in the mothers of my friends.
Also reading the book "Pollyanna" put my problems - real or perceived - in perspective. Even as a near-teen I considered myself lucky. I only had to live with my mother for another 7-10 years while she had to live with herself forever.
Know that you are in our hearts, thoughts, and prayers as you work through this stage in life.
Love you!
Smart Red