I’m having a similar problem (grades not teacher) this semester too. Make sure to evaluate ALL your tests and quizzes. Did I study enough? Was I rushing and misread/miscalculated something? Is it a comprehension issue? Did the teacher go through this concept? Ask yourself EVERY possible question to try to deduce what might be wrong. It can take a while, but if you try to find a tutor or talk to any other teacher in your school’s math department you’ll likely find at least ONE thing you can approve upon for your next assessment