tranSit in china. travelling to nepal

Hi. Im nepalese citizen. now living in japan.i have valid visa for japan till 2017. i want to go back to nepal on oct 20 2014 via china.my passport will expire on 2015 feb. i dont have 6 months in my passport.
can i travel to my country nepal with my passport and come back to japan again with the same passport?
or i can make new passport in nepal while im there.
is there a problem in chinese immigration because i have 2 transit in shangai and kuming. which is for 14 hours.
any 1 plz help me .
thanks
KP