I will start off by being honest and saying I struggle with anxiety. Always have even as a kid so it is one of my worries that my kids will suffer themselves or pick up stress from me. I might therefore be over analysing this.
My three year old is a usually very happy very energetic boy but can be shy occasionally. We try and get him out everyday to let off steam.He has recently started to seem completely on edge sometimes. He will grind his teeth, play a bit too boisterously or pinch or hit but not maliciously. It's more like he is tensing and can't keep still so needs to let it out. As a kid I used to tense up my whole body until it hurt then release as a way to relax. It's not quite like this but similar. He gets right in your face and usually wants a cuddle but can't keep still.
He has also started to say stuff like he hates us and wants to live with grandma. I think this feels like he is trying out stuff he has seen at preschool or attention seeking. Nursery have said they want to work on him expressing emotion as he can get a bit frustrated. He has a seven month old sibling but this has only been going on the last month or so and he never showed any signs of jealousy before really.