How long does it take you to drive that five miles ?
Lots of short trips don't allow the engine to fully heat up and burn off the fuels that gets into the oil. Over time this is what will damage your engine. One good thing is a modern engine heats up quite fast. But still I would be changing your engine oil more than once a year. Maybe change your oil once every two months.
IF you could drive the car for say 30 minutes once a week or so... that would really help burn off the water and fuel that gets into the oil. That would be better for the engine in the long run.
