Worsening UTI Symptoms but no UTI?

Hi guys! Discovered I had a UTI on the 14th of June but wasn't given the correct medication until the 30th. Was given one sachet of Fosfomycin which did nothing to clear the symptoms, so started another on Monday (6th July). On Tuesday my symptoms were getting worse with really bad flank/back/groin pain, so was told to start taking a weeks course of Nitrofurantoin, which again, hasn't seemingly helped.

I've just got back from waiting 11 hours at the hospital and after having blood and urine tests done (I also did a sample for my GP on Tuesday where nothing was found), I was told i don't have a UTI anymore and they're not sure what the issue is. Doctor said he's positive I'm not at risk of a UTI or Kidney Infection and said it's up to me if I finish the Nitrofurantoin course, and he assured me it'd be safe to do so.

I'm just so confused and honestly a bit scared because the pain is really bad and I'm worried about kidney stones. I'm from the UK so it's a bit difficult for me to go and see a Urologist, as I'll have to wait months or pay ALOT of money (which I think is going to be the case unfortunately)