I'm usually an above average student but …

I'm usually an above average student but lately I've been having very low grades in all of my classes because I am unable to focus in class. I told my mother but she feels I am making an excuse as to 'Why I don't do my homework' and that I am trying to gain attention. She believes I am acting out and will not take me seriously, blaming my bas grades on not doing my homework. I've never had this problem before so that is why she believes this. What should I do? I hate fighting her of all people.

Try talking to your teachers about strategies to use in class.  They may notice some things that your are unaware of.  Explain your situation to your mother and explain your feelings.  If it is something beyond your control, you can also talk to your doctor.