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It is probably just a urinary tract infection, unrelated to the spay. Please bring a fresh urine sample to your veterinarian for analysis. Better yet, have your vet obtain the urine by a cystocentesis (needle into the bladder), this way if it comes out as a urinary tract infection you know that it is totally unrelated to the spay.
If just a urinary tract infection, a culture and sensitivity of the urine with appropriate antibiotics and other medications should solve the problem.
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