[Gammix]

pawn Код:

#define HOLDING(%0) ((newkeys & (%0)) == (%0))

Is only called once, its registers an instance when you start holding the key and exists until you release.
So i guess you are looking for a back to back calling, for that case, declare a timer when player starts holding and then do your code in the timer. Also, when player RELEASE the key, kill the timer.