I physically can not start my homework

I'm not diagnosed, but I'm 99% sure I have ADHD.

It feels like I physically can not start my homework. My mind wanders off to another topic, and boom, 30 minutes gone. I've tried to explain to my mom, but she says "Just do it." My dad told me to take a break as needed, but I still have to tell him about the time flying past my head. I had this problem for a few years, but if a 5th grader doesn't do their homework, they are just lazy, like what I am labeled by my parents and I assume my teachers. Please, help me.