A pus cell count around 57 per hpf usually points to some urinary inflammation, even though your culture didn't grow a specific bacteria this time.
Next Steps
A repeat urine routine and culture after a few days, along with a pelvic exam, can help clarify if this is infection or a gynaecological cause.
Health Tips
Please avoid starting antibiotics on your own, since a negative culture still needs proper interpretation from your doctor.