my 2years old son is sucking on his lower lip ...?

[baraem]

hi everyone,
my 2years old son has just started to suck on his lower lip all day and night, i don't know where it came from, he never had a pacifier, or a botle, he nursed for 12 months, he eats regular foods, and has been drinking from a sippy cup from about five months, will this sucking go away? he also stop eating his food just has no appetit.
Additional Details
will the sucking damage his lip or make it drop or longer? I'm worried i don't want my little boy to have an ugly mouth

Mine did this for a few months at around the same age. Grew out of it. Main problem was that because it was in the winter it caused dry, broken patches of skin around his mouth. Cleared up by using vaseline/epaderm though.

Don't worry about it.

that s what i thought at the beginning but his behaviour change as well he become more sensitive then before .