Hi, my daughter was 3.9 years old. she always chewing or bites his lower lip .. lip size is increased slightly due to biting. i remind her every time when i saw her doing it. but no use , after 5min again she bites her lip. please give me suggestion how can i stop her biting her lip. is it compulsory to consult a doctor for this problem?is this a serious problem? why she doing it? Thank you.