I hope these sentences give you an idea of how the past continuous has a different function to the past simple. a) "I wore a jumper yesterday" - simple description of a past, finished event - past simple b) "I was wearing a jumper yesterday" - emphasises the progressive nature of wearing over a certain period of time. But in practice, the meaning is the same as a). c) "I was wearing a jumper at 10am yesterday" - at 10am I was in the middle of a period of wearing a jumper. I put it on at say 8am and took it off at 9pm. d) "I was wearing a jumper at 10am yesterday when my friend called me" - at 10 am, I was in the middle of a period of wearing a jumper. This tells the listener what was happening (progressive actions) around the time of a specific event (the phone call).

As far as i know, if you use the past continuous, you will keep it with a sentence...