I have been peeing my head off every 5 minutes for weeks now. Finally got round to visiting the GP and he did a dipstick test which showed not much and prescribed a one off treatment for thrush because I'd treated myself for it 2 weeks previous and he said that perhaps that was causing it.
He told me to put an MSU in, which I did, but still peeing my head off and it was getting worse.
Did some research online and found that it was probably cystitis which I had ignored before because I thought that cystitis burned when you peed, which I wasn't experiencing.
Pottered off to chemists and bought some potassium citrate, and bingo, 48 hours later, no cystitis and no peeing my head off anymore.
Why couldn't the GP have suggested this 2 weeks ago? 
and they don't like you doing your own medical research on the 'net.....
The GP never manages to treat anything I turn up with, I don't know why I bother really.