We booked a GP appointment btw (not today). It's on Tuesday. We described the symptoms and we were told it didn't need an emergency appointment. I wanted an emergency appointment but was reassured for sure, am now doubting myself!
DD3 is 4.
For about a week and a half, she has:
Had headaches. This is most common in the morning, but it can be any time tbh. Not constant and usually a few days in between, and the pain seems to fluctuate a bit (she said it hurt then hurt a bit less then hurt a bit more etc;).
Some vomiting. Not severe, constant vomiting, just occasional spurts. Again, more common in the morning. Every few days, sometimes on days when she gets headaches but sometimes not.
She is clumsier. With her walking in particular. She's not the most coordinated child in the world but is a bit stumbly. She says she isn't feeling dizzy, but her legs just flop. 
She is pretty tired and feeling kind of floppy (weak? She said she felt floppy, not entirely sure what she means, and she isn't good at explaining stuff!) and exhausted. I'm guessing this could be caused by an under the weather type feeling from the other symptoms.
She's very irritable. Again, probably caused from tiredness and other symptoms.
Her words are a bit muddled. She is delayed and struggles verbally, and sometimes struggles more than most. This is probably caused by being ill as she gets less verbal/makes less sense generally when she's ill.