Talk to Gastroenterologist on Urinary Inflammation

I am asking about an issue which has been affecting my 12 year old daughter for the past 3 weeks. She is prone to having recurrent UTI's but for the last 3 weeks, she has been in a lot of pain, it gets better for a few days but then again she gets bad days.

Basically when she pees she feels burning, even when she is not in the toilet she suffers from continuous burning and makes her unable to walk or sit normally. She does not have any back pain so kidney's are fine (as per the GP). Her urine was tested yesterday and came back with no bacteria or blood. But the pain is alot, affecting her ability to go to school or perform her daily activities. This discomfort/pain comes and goes, she had an antibiotic course a week ago (can't remember the name) but it made no difference at all for her.

Doctors have been unable to identify the root cause for the issue, I have been giving her cranberry juice once a day as advised by GP, also she drinks 2 to 3 litres of water daily. Please let me