Hitting phase

My son is 20 months old and he has recently started hitting/kicking/pulling hair he does it to us (me&dad) but he also has started quite frequently doing it to other children too, often very randomly, sometimes it’s clearly linked too frustration (he doesn’t want to share etc) and sometimes it’s sort of rough and tumble play like he does with his older cousin (she’s 6) and he clearly hasn’t understood who/when to rough and tumble🤦🏻‍♀️🤣 but often it’s just random he’ll just pull a kids hair or hit them or throw sand or something at them. There’s no reason for him to do this he doesn’t see violence and I try to do gentle hands and hands are for hugging etc but he just hits and then strokes 🤦🏻‍♀️🤦🏻‍♀️🤦🏻‍♀️ I remove him from the situation and redirect his attention, it’s been about two weeks now of this and I’m really getting quite stressed out (probably being 6 months pregnant adds to the stress) and it’s starting to get to me because I don’t know how to change this behaviour. Lots of people saying it’s just a phase but no other kids his age seem to be doing this nor do the other kids at the park etc so yeah any advice or words of kindness would be great haha I’d like to add I definitely think it’s a phase because for the same period he just whines and whinges and cries about everythinggggggg and he was never like that he was so like breezy until about two weeks ago and now I have some sort of Tasmanian devil 🤣🤣