Prevacid/Lansoprazole for Heartburn?

Have any of you taken over the counter Prevacid or Lansoprazole (generic name) for heartburn/acid reflux during pregnancy? My OB recommended it (I think it's a category B drug) and said I shouldn't stop taking it at any time.. But the directions say only to say in 14 day doses at a time, so I'm a little confused.. and just curious to hear your thoughts on it if you've chosen to/not to take it..