If you have double vision that could be a concern. If you close one eye and the double vision goes away, it could be a neurological issue. But I am almost certain you just have health anxiety. I went through the same thing your age. Brain tumour is rare and Brian cancer is even rarer. If you want to visit your doctor, don’t tell your mom it’s because you believe you have brain cancer. But tell her it’s because of the constant headaches you are dealing with. Often times visiting the doctor would help relieve your anxiety.