5 days may not be long enough for it to settle in and be ready to feed. They are all different, some take quickly some take longer. So don't panic.

do you know what caging, substrate and so on it is used to. It will settle in quicker if there is a similar environment. What kind are you using?

Are you sure you have the right humidity, temperature and so on?

Did you heat the mouse up to body temperature with a hair drier or hot water?

Keep an eye here, others will have lots more advice and questions to help you.