My driver door and rear passenger doors don't lock on my 2005 Escape.

My 2005 Ford Escape has been having problems with the driver and rear
passenger doors. When I lock the car using the key fob, only the hatch and
front passenger door lock. The rest remain unlocked. I found that out when
my car was locked and my dad opened a rear door. Most of the time, the
alarm goes off but sometimes it doesn't. Does anyone know why the doors
are not locking? Also, I've only owned for the past 3 weeks.