UTI. Be sure when you finish the meds, that you take a urine sample back in to your vet and he gives her a clean bill of health.

If he mentions anything like:

I THINK we got it all cleared up, or
There is a little bit of crystals left, but they will go away once the rest of the medicine goes through her body...

Then insist on continuing the meds for another cycle. From experience (and on the words of my "specialist" vet) if the infection is not treated completely or if there is any doubt, this will turn into a problem.

Jazz was being treated with one when we adopted. We finished the meds, and the vet (a new one at the center) stated there was some minute crystals left, but the medicine in her system should clean it up. YEAH RIGHT!!!!!!

2 months later she got another infection. I took her to our vet specialists and she told us the other one was never cured. Fortunately, she put Jazz on a stronger antibiotic, but on 2 cycles. We did another sample, with no residue. YEAH.

The bad thing about not ensuring a clean bill of health, is that left untreated, or not cured completely, can cause health complications in other organs.

Just make sure you take a sample before and get a clean one after meds.