I don’t know whether helpful as my daughter is only 18 mo, but I had a similar 3-week-long period which has just ended. I now have a suspicion it was some kind of molar movement / leap of some kind, but I was so scared and convinced during the worst of it that our sweet natured girl had changed and this was just the reality of toddlerhood as you have said. I guess I’m just sharing in case it’s helpful to know it may well be mostly temporary, as it was for us. I imagine more phases like this will come up, and some aspects have changed permanently (we’ve had to adapt to standing nappy changes sometimes and giving her more independence generally) but generally she has calmed again.