Have just had a lightbulb moment.
DD (3) has been ill since Tuesday - vomiting, high temperature, abdominal pain, screaming that her bottom hurts. Took her to see the GP today and he gave her antibiotics for her chesty cough. 
She has been screaming a lot for most of the day and about 10 mins ago when she had woken up screaming again, I managed to get out of her that her it was her "front bottom" that hurts. I asked her if it hurt when she did a wee, and she said that it did.
So I am 90% sure that she has a UTI.
Question is, how likely is that the antibiotics I got from the GP are going to work on her possible UTI?
Also, is there anything I can give her now that will alleviate the pain?
Any advice gratefully received. Thanks in advance.