How do I tell my mom what's wrong?

Lately I've just been feeling so down about everything. Everything makes me just want to scream and throw something against the wall, I've been snappy because of it and when my mom asks me what's wrong I just tell her I'm tired because I can't think of what to tell her that won't sound like I'm attention seeking. I've had to go to therapy before and I hated it. It just made my mom cry and that is the last thin I want to see in the world and I feel if I tell her she'll get depressed. She's on Prozac as it is and the last time I was in therapy she was severely depressed and blamed herself. How can I tell her without making her blame herself?