The way math is taught these days is not direct or straight-forward, making it extremely difficult for ADHD kids to see the big ideas and become fluent in procedures. Currently, math is taught in group settings where you and your classmates “discover!” for yourselves the equation for a line and somehow, how to do two-column geometric proofs with a worthless textbook absent of any examples. There is simply not enough practice in math classes from the last 5-6 years to automate procedures. This is important for the reasons you describe: no topic in math these days is taught and practiced to mastery. The cognitive load and memory (both maxed out when ADHD kids are doing math) are taxed, not allowing you to learn new concepts before your eyes.
Please find a competent math tutor, someone taught in the older, traditional math procedures. Is there a parent, grandparent, Aunt, neighbor that has a science or engineering degree to help you? Pick up a cheap, used Geometry book on Amazon from the mid-1980’s (I recommend Dolciani). Stick with it! It’s not you, it’s the crazy curriculum. Don’t give up – math is power and will open doors for you later.