a cause of chest problems (maybe bronchitis too, i'm not sure) is "shallow breathing",
u might not notice but while at the pc, u tend too relax too much and tend not too take deep breaths but breath more with frequent shallow breaths which don't do the lungs any good whatsoever because u aren't using them at anything like their full capacity.
i was doing this particularly while playing internet games, i get too engrossed in them.