Definition: (informal) If part of your body is playing up, or plays you up, it is painful. This is used with chronic or long-term illnesses or injuries.
(This phrasal verb has more than one meaning)
E.g.1: I can’t come to work today – my back is playing me up again.
E.g.2: When he was younger he injured his knee playing football. Now, during cold weather, it sometimes plays up and then he can’t walk.
This phrasal verb can be separated by a pronoun (E.g. 1)