This could be a learning disability called Dyscalculia. It’s common to co-exist with ADHD.
Find someone at school you can confide in about this — the math teacher or a guidance counselor. Let them know that you’re trying super hard and struggling. Because you go to someone and ask for help, they’ll know you actually are really trying.
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism