Sorry to hear you are seeing a recurring problem with the urinary tract. I am glad to see that you have scheduled another appointment with your veterinarian.
I agree with Shayasmom. A urinary bladder radiograph is important when we see blood in the urine that either does not go away or returns after treatment. Uroliathiasis is a potential cause of persistent blood in the urine. The two most common stones we tend to see are struvite or calcium oxalate stones. Sometimes, the urinalysis will not show blood or crystals.
If the radiographs are normal, I will recommend to my pet owners the option of running routine blood work (CBC and profile) as well as a culture and sensitivity of the urine if the lab identifies bacteria. This is done via a cystocentesis (needle in the bladder to collect urine).
Ultimately, if all the tests are normal, an abdominal ultrasound to look at the kidneys and bladder would be recommended.
If your pet is not spayed, your veterinarian will also be able to evaluate the uterus to determine if there is an infection present or not. The post does not indicate whether she is spayed or not.
Good luck and I am sure you and your veterinarian can determine the best course of action.
I would ask them to do a xray. My pug did the same thing and they gave her antibiotics and it just didn't seem to clear up then it started to where she would try to pee but it would only be a few drops. I took her back to the vet and they finally did a xray and discovered she had a bladder stone. They were able to do surgery to take the stone out and she's been fine ever since. If that's not it I would maybe see if they can culture the urine, I know in people we can have different strains of infections and some are resistant to certain antibiotics. Hope that helps.