White Carrara marble has yellow stains

I installed a White Carrara marble in my bathroom. After a year all the marble has yellow stains. I would like to know if it is something wrong in the installation. Or the quality of the marble, can there be bad quality marble Carrara or all white marble stains yellow. Or is something wrong in the surface where the marble was installed? Can there be some kind of water filtration? Or fungus? How can I fix this? and return the original color of the white Carrara stone? Thanks, Beatriz, July 12