The short explanation
New fever and pain in the back or side after starting treatment for a bladder infection can mean the infection has reached the kidney, or that the bacteria are not responding to the medicine you were given. Either way, this needs a clinician to see you today, not tomorrow. A kidney infection usually needs a different or stronger treatment, and sometimes hospital care. Do not simply switch to another medicine from a pharmacy or double up on what you have.
What depends on your situation
The parts of this that change from woman to woman. Uncertainty is stated, not hidden.
- If a urine culture was sent at the start, the result may already show which medicines the bacteria respond to; ask your doctor or the lab. If no culture was done, one is usually sent now.
- Pregnancy, diabetes, kidney stones and any kidney problem make this more serious, so mention them. Doctors may do blood tests and an ultrasound to check for a stone or blockage.
What this answer cannot determine
The boundary of online education. These need a clinician who can see you.
- This answer cannot tell whether the infection has spread or why your treatment is not working. That needs an examination and tests.
Questions for your clinician
Take these with you. You can add any of them to an appointment card.
- Has the infection spread to my kidney?
- Has a urine culture been done, and do the bacteria respond to my current treatment?
- Do I need blood tests or a scan?
- Do I need hospital care?
When to seek help
Clinician-approved guidance for this topic. When in doubt, being seen is never the wrong choice.
Emergency — call 112 now
- Call 112 or go to the nearest emergency department if you have shivering with high fever, feel faint or confused, are breathing fast, cannot keep fluids down, or pass very little urine.
Get help the same day
- See a doctor today for new fever and back or side pain during treatment for a urine infection.
Raise it at a routine appointment
- Once you recover, book a follow-up to make sure the infection has cleared and to discuss why it spread.
Sources
The evidence this explanation is built on.
- Kidney infection NHS
- Urinary tract infections (UTIs) NHS
- Urinary tract infection — adults MedlinePlus (NIH)
Who wrote and reviewed this
Every AskHer answer names its author. A clinically reviewed answer also names the clinician who signed it off — if no clinician is named below, it has not been clinically reviewed.
- Author
- AskHer Editorial (AI-assisted draft) AskHer's editorial team — not an individual clinician Works in English, தமிழ், हिन्दी
- Clinical reviewer
- Nobody yet No clinician has signed this answer off, and no person on the editorial team has read it yet. That is what the “Written with AI assistance” label means. It is queued for an editor to read, and then for a clinician who works in this area. The sources it was drafted against are listed above.
- Review status
- Written with AI assistance — not yet reviewed by a person
- Last reviewed
- Not yet reviewed by a person
- Version
- 1
Correction history
Substantive changes are listed, not quietly edited away.
No corrections have been made since this answer was first published.
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