Stop your singlish and don't eat your words

I've been hearing mummy telling me not to speak Singlish. I have been telling her "you see lah, you see lah......" Mummy stared hard at me and told me there's no 'lah' in a dictionary. And then yesterday I was telling her something and she couldn't understand me. She told me not to eat my words and speak properly.
Is there anything wrong with my language? All my friends speak in the same way.