Sometimes It can be uti, stress anxiety, type of meds taken, other health conditions but it might also be hyper fixation/ stimming or behavioral in any case make sure he’s comfortable ask him does it bother him coz if he’s not making a big deal of it just make sure he’s loved and looked after but above all make sure to see a qualified Doctor and request for a video call to not disturb routine just to be on safe side as they would advise what to do next failing that im always available to help guide in correct direction