Not all infections show on a lab result, you could still have a UTI.
Or it could be VA causing the symptoms . Have a look on the Newson website and join The closed vaginal atrophy group on Face Book. The ladies there are very knowledgeable on all down below issues and can point you in the right direction.
Vagifem can cause irritation. I would also go to a GUM clinic as they have test facilities on site as some vaginal conditions can cause an irritated bladder , as can stress. Cytolitic vaginosis can cause bladder issues.
Try not to worry. It will get sorted once they find the cause.
PMXX