Perhaps you are not shy, but you somehow get shy when talking to your mom.
This could be because you press yourself into causing an impression, or because you are being hard on yourself - perfectionist maybe?
Don´t be. I once took English conversation classes, a teacher would make us watch a movie, Phone Booth (por um fio), for instance. Then we would discuss it.
I am usually shy, for that matter; but those movies and our will to express ourselves in English would make us to talk in English, bad or good English, but we could get by.
The downside of that classes were that two hours were like minutes, time really flew there and then!