Power locks problem

I have a 1998 Ford Expedition XLT with power door locks and for the last 6 weeks the locks have been acting up. At first the door locks would lock after I opened the door and was getting into the truck, even before the truck was started. Now I have a problem that the locks immediately lock as soon as I use the key fob to open the doors so I am sneaking into the truck by using the key to operate the lock and jumping into the truck, sometimes the locks cycle for a few seconds trying to lock but they are already locked. All 5 doors are doing this at the same time. Any ideas?

My problem is that my 99 exp won't lock after it is being driven down the road and the door ajar light is on even if all the doors are confirmed closed. Can anyone help with this one?