Is it normal i think my mother thinks i'm stupid?

You know what mate? I used to think the exact same way. Tried to be smart to inpress her for a while. Then I made this descion to quit giving a fuck. Thats what I did and it don't bother me no more. Try it mate.

Well if she's never actually said it then you could just be imagining it. Or she could just be babying you regardless of how smart she thinks you are, a lot of mothers do that.

Sometimes parents push their children more than the child is comfortable with because they know that you grow from stress. Other times, they are just bad parents. Only way you will find out is by asking her.

Ask her straight out.