I'd never had a UTI in my life untill recently. I had two...probably the same one not cleared up..within three weeks. I then had two episodes of severe pain where my left kidney is.
Today I had a kidney and bladder scan which has shown a small stone in my left kidney. It would appear that this has been the cause of not only the pain but also, perhaps, the UTI.
Incidentally, my GP told me cranberry won't help once you have an infection but may help prevent one taking hold as there's 'some' evidence it stops bacteria sticking to the bladder wall. She wasn't convinced and neither am I but I've started taking one cranberry tablet daily...can't do any harm even if it doesn't do much good.
Hope you get it sorted.