smoke lowers ur immune system, when i been smokin a hellofalot i usually get colds, or chest infections and shit, the only way to get rid of them is to quit smokin until u feel ok again.. i used to hate hittin a bong coz id caugh like a motherfucker too coz of some chest infection.. i used to hock up a load of yellow phlegm too, it was fucked up.. so i quit for a bit, took a load of antibiotics and i was ok..