I won't make it past 18

(15)m I grew up in a loving abusive household after my parents divorce I live with one of them for a week and rotate on Monday. My mom constantly pushes grades onto me and just recently told me I can't get anything les than a B+ on any of my work. It's not like a have a history of high grades she just wants me to be like she was. She was a all A student through elementary to highschool, but I have ADHD she has refused to medicate me for and I feel like I can't do the things she wants me to do. Everyday I'm with her I feel like shit because it makes me feel like I can't do anything right. Even my teachers think the the same and I feel like I'm being buried in expectations that I can't reach. I lost all my friends I've had since 6th grade in less than a month and I feel like life would be better for all involved if I wasn't here.